OK, I leave to someone else the plausible route to US acquisition of any of the Portuguese territory, though I do also suggest that Goa would almost have to be a package deal for the trifecta of all three Asian colonies--Macao, Timor and Goa.
I want to focus on the post-WWII situation, in which both Macao and Timor would have been of course conquered by Japan, but liberated and restored to US territorial status during the war. Goa of course would be quite safe in retrospect, though of course during the scary time of Japanese ascendency, around the Axis riding high in 1942, there would be some fear the Japanese might get that far. Presumably Goa plays a role of some distinction during the war, assisting the general usage of British India to supply and forward supplies to the southeast Asian fronts, serving as a rear repair facility for USN and Commonwealth (and other allied, DEI for instance) shipping. Goa would be eclipsed by the major British facilities in Ceylon as it was called, but might serve a valuable role as a backup overflow site for the combined allied navies.
What interests me is the question of US territories as a whole. I've allowed what I think of as a rather splendid vision for sweeping electoral reform in a proportional representation direction, for House, Senate and even the US Presidency, to get entangled with the notion of complete representation of all peoples subject to US rule in Congress, House and Senate both (and a role in electing the President).
Let me disentangle them for the moment, though another TL on another site did in fact propose the introduction of PR at a Federal level in the immediate post-WWII era too. Setting aside proportional representation, let's consider how perhaps the expanded US territories, in India, Indonesia and China, might conceivably leverage a post WWII reform introducing Congressional and Presidential electoral representation for all territorial citizens as well.
I've mentioned Truman's advocacy of a better autonomy and relationship with Puerto Rico already. Were there a resolution to keep the Philippines under the US flag as well, the problem would grow larger. But Philippine independence was a done deal before WWII broke on the USA. However, supposing the three Portuguese colonies were all firmly in US hands, independence for them is much more problematic. Puerto Rico as a sovereign nation actually makes some sense but how can Goa, Macao or Timor hope to fare?
I assume then whatever treaty there was, does indeed mandate the USA not alienate the former Portuguese colonies to any third power. Nothing would stop the USA from breaking that obligation if we really wanted to of course, but it serves to help explain how the status of all three remain firmly US.
The time window is before Mao takes complete control of China and thus the matters at hand might be settled before the PLA comes knocking on the gates of Macao. This would obligate the President, surely Harry Truman unless one wants to throw curve balls, to defend Macao, and since at this point the British would hardly want to or need to surrender Hong Kong, economics and logistics of defending Macao in a hostile relationship with the mainland are probably workable. Indeed in the face of this obligation the USA might well be forced to lend Chiang Kai Shek considerably more aid, and an enclave surrounding both colonies and indeed including Canton might be maintained--technically three governments then, a rump RoC under Nationalist rule holding Canton and a cordon shielding both HK and Macao from direct contact with the PRC. I know there are people who are sanguine about the USA being able to defeat Mao handily across the board, but I am hardly one of those people; I assume despite much increased US aid Chiang collapses and is only able to hold around Canton thanks to massive US assistance including threats of A bomb attacks. The status quo that develops then is a massive influx of anti-Maoist Chinese and exodus from the RoC zone of pro-Maoists, and the enclave more or less stabilizes as a deeply resented thorn in the side of US-PRC relations--but that is much as OTL anyway. So Macao can survive long term on its limited territory under cover of a US propped up RoC enclave in addition to Taiwan. This obviously has major geopolitical knock ons down the road and I would not rule out the eventual surrender of Macao to the PRC many generations hence, but for now let's roll with it.
Timor is of course quite secure from anything the Indonesians might do for the same reasons I argue Goa is. OTL eventually Indonesia came in as a US client under a US backed coup, and a decade after that when Portugal abandoned Timor Gerald Ford, at Henry Kissinger's advice I don't doubt, signed off on the Indonesians taking Timor by force--something Ford contritely apologized for later in his life, too bad he didn't have that moral clarity at the time. Suffice it to say the Timorese did not much appreciate the new regime and fought it bitterly for decades, and eventually won their recognized independence again. I am also of the opinion Saddam Hussein might have had this precedent in mind and believed the USA would back or anyway accept his seizure of Kuwait, so it was a real case of sowing dragon's teeth. A USA owns Timor TL at least spares us all this horrible mess and might have had important consequences in 1990, perhaps preventing even worse that we are still reeling from today. Thank you ever so much, George Herbert Walker Bush.
So anyway--back to 1945 or so. Truman, amid a lot of other pressing concerns, has in the back of his mind the notion that the Puerto Ricans have had a raw deal. The Philippines are being let go, with our blessing, well and good, but the USA has just acquired a whole boatload of formerly Japanese ruled territory in the Pacific atop our regained former possessions such as American Samoa. It is conceivable that eventual statehood for Hawaii might possibly scoop them all up in one gigantic American state of Pacifica, but many of the new islands are UN Trust Territories, we can't legally just do as we please with them. In addition in this ATL, we have three former Portuguese territories. Let's vaguely stipulate we got ahold of them in the 1880s, before the Spanish American war (but greed for the superior potentials of Manila as a base, plus the value of the Philippine hinterland, still motivated the seizure of the Philippines anyway, despite our already having a decent base site at Timor and direct access to China itself in Macao). For over sixty years then, barring Japanese occupation, these small territories with their distinct populations have been under the US flag, their sons joining the Navy and Army and Marines probably, their entrepreneurs dealing in their shadowy insular status as semi-citizens. The Timorese and Macauvians have suffered much loss at Japanese hands but also provided some wartime heroes of resistance. They have among them radical revolutionaries but only the ones in Macao have a strong case and that only for being absorbed into a larger whole where their distinct Portuguese and Yankee influenced identities would be swallowed up. Only radical minorities are really interested in that. Wartime expedients have largely won over the Goan former radicals, also a minority even before, and political restiveness in all three is thrown behind achieving better status as US citizens.
Statehood is out. I have not yet surveyed either the modern or then-contemporary populations of any of them, but am guessing Goa and Macao are quite tiny to be states. Maybe they exceed Wyoming's population? I should do the research. Let's stipulate they don't. Timor I think is just on the cusp of being state-sized maybe. It might make sense to make Timor a US state, but then Puerto Rico certainly should too.
Let's say then that with the additional three territories thrown in to the mix, Truman resolves to make a clean sweep of all the odd corners of US subjects deprived of the full powers of citizenship. The additional numbers, the diversity, and the recent wartime role of the three south Asian holdings help his political case. He needs an Amendment to the Constitution, but these were coming pretty fast in the mid 20th century.
Rather than being restricted strictly to statehood, then, the Amendment would allow for the possibility of kicking the can of statehood down the road while granting the various disfranchised groups comparable enfranchisement. It would specify conditions and terms under which territories can be granted representation in Congress, House and Senate, and voting for the President, without being actual states and while in some respects remaining under the control of Congress as a whole.
1) Alaska, Hawaii, and Puerto Rico are to be included in the general apportionment of all House seats. As a political expedient, the current apportionment of 435 House seats is raised so as to guarantee the standing 1940 census apportionment of the 48 continental states remain the same, so no redistricting is required immediately there. The former two remain territories in the usual sense, the Commonwealth status of PR is Constitutionally specified in the same amendment, with PR having a right to either petition for normal statehood, retain a special Commonwealth status, or seek full independence at a later date. In either of the former two cases, PR is counted in the Census (as indeed the Territories are anyway) and under the new expanded House size would (in modern times, don't know yet about late 1940s) would receive House seats in number between Oklahoma and Connecticut, that being the population now in the 2010s. Have to research which states it was comparable to then. Alaska and Hawaii at this early date would be of a size to get a single House seat anyway.
Depending on what their populations were in the late 1940s, Timor, Macao and Goa might also be state sized. If so, they too would be granted quasi-state status for purposes of House representation and Commonwealth status with option for statehood--independence might be ruled out by the treaty by which they were acquired as stipulated however. But all are pretty small and badly situated for independence anyway!
Puerto Rico is immediately granted two Senators, of the same status as any other US Senator despite the not quite state status of their constituency. Since Alaska and Hawaii are clearly headed for statehood too, they too can also have two Senators; in this way the three Senate classes which each had 32 members OTL until the admission of these two states can remain balanced with 34 members each for a total of 102 Senators, a number divisible by three.
It is interesting that there are also three Portuguese territories--if all three are state level of population, they can also be granted two each for another 6 Senators evenly spread around the classes, each of which is now 36 for a Senate of 108 members.
Under the Constitution, of course, each state has Presidential electors in the number of their Representatives plus Senators. So this process would add say 7 EV for PR, and 15 for Alaska, Hawaii, and perhaps up to three former Portuguese territories around the south of Asia. Note we are expanding the House size to avoid redistributing the established 435 for the lower 48 states.
However, there is a monkey wrench in the works!
The idea of the Amendment is guaranteeing everyone who is subject to US power on a permanent basis must have representation in House, Senate and electing the President. We still have the District of Columbia and the smaller territories in their diversity to consider.
DC of course has been kludged in to the Presidential race alone via a special Amendment OTL, so I think there should be little Constitutional doubt these maneuvers are possible, if politically desired. Here it is specified to have a permanent non-state status, not a Commonwealth but subordinate to Congress formally, but granted rights of autonomy similar to OTL and guaranteed proportional House seats and two Senators. There goes the lovely threefold symmetry! We will then have one class of 36 and two of 37 for 110 Senators. DC has always been a medium small state in size, never (well, not since the 1930s anyway) smaller than the smallest state but never I think big enough for two Representatives, but we can leave that open for future population shifts--it hardly seems likely it can grow that big without tremendous densification to be sure. Realistically it will have one Representative and two Senators and thus three EV for the foreseeable future. This Representative like the estimated 10 for the above mentioned future states and Commonwealths is extra, so say we are at 11 so far.
Finally...there are the smaller territories, each so distinct that merging them is not reasonable and each so small they should not be considered states. Collectively the four inhabited remaining territories as of the 2010s--in population order Guam, North Marshallese Federation, US Virgin Islands and American Samoa--are considerably smaller than Wyoming. They cannot then be a state even collectively, and it makes little sense to lasso these three disparate sets of Pacific Islands and one in the Caribbean into one state. As mentioned, someone might consider lumping the three island groups in with Hawaii, but culturally and logistically that makes very little sense. Samoa, the smallest, has some cultural historic connect to Hawaii being also Polynesian, but the connections lie a thousand years and more in the past, and the distance from Pago Pago to Honolulu is I would guess greater than that from Bangor Maine to San Diego California. Guam and the North Marshallese might conceivably be federated into one sprawling west Pacific set, and with some historic cultural connection between them, but again that is centuries out of date and broken up by shifting political possession. The US Virgin Islands are of course in quite another hemisphere--it might be argued they should be merged with Puerto Rico but I think both Puerto Ricans and Virgin Islanders would protest that pretty strongly!
Territories remain territories then. They are too small to be states by far, though it is possible and reasonable for them to have autonomous local self government as indeed these four groups of islands do today.
The Amendment then would do a very small violence to the proportional representation (in the sense of states having Representatives proportionally to their population) by granting the entire set of all remaining miscellaneous territories that have no path to either statehood or state sized Commonwealths one collective Representative they all get to vote on. This overrepresents them but does no harm really, and guarantees everyone who lives under the US flag has a Representative.
Now one concession to the small population of this miscellaneous grab bag is that instead of the proportionality principle being applied to the House representation, they have a presence in the Senate...but only one Senator.
This is rather unfortunate--I had as I said a yet more grandiose plan to integrate all this total inclusion with proportional and quasi proportional schemes for House, Senate and Presidential election I have left out here; in that system a more balanced way of giving the people of the Territories a fair shot at voting for representation with some frequency comparable to people in normal states emerged. But not here. They have only one Senator.
But consider this. I set up an increment in bodies each having two Senators, numbering six, adding twelve Senators to 96 and thus remaining divisible by three and giving rise to three classes of 36 each, but then threw in the monkey wrench of DC creating imbalance of classes. But putting a single Senator for the Territories in the third class raises all three to 37 and makes the Senate number 111, a number divisible by three.
Suppose my count was off, and we had only 5 two-Senator sized bodies being admitted to Congress, so we had 106. Then we would have one class of 37 members, and two of 36. Adding one would leave it lopsided with two of 37 and one of 36. What to do?
Well, suppose the Territorial Senator suffers another indignity. Their term depends on how imbalanced the classes are without them! Suppose we have one class larger than others. The Senator from the Territories can instead of serving one six year term, be subject to election for a two year term and then for a four year term, skipping the largest class, thus restoring the balance in terms of how many Senate elections occur each cycle. If balance would have been fine without them, they can serve two year terms, having short terms like a Representative, but sitting on the Senate.
Either way, the citizens resident in the small territories lumped together in this way would thus receive 2 EV, one less than any resident of any other polity...but considering their small population, they would actually be again a bit overrepresented in voting for the President.
The territorial situation in the Pacific would be somewhat more expansive in 1945 to be sure. Several former US Territories there have since been spun off as independent nations in more or less association with the USA; in the late '40s these would be recent acquisitions under USN effective control. This of course is where we did US atomic and hydrogen bomb testing, in addition to the deserts of the southwest.
A complicating factor is that some of these territories I believe were under some sort of UN mandate. However under the rather sparse degree of influence my proposal gives the territorial subjects as provisional US citizens, it seems to do little harm and some political good to allow people who might later achieve independence to vote for US Congress and President as part of the widespread net of generic small territories alongside others for a grand total of one Representative, one Senator and two Presidential EV. And including them in this way might turn their inclination toward remaining US citizens indefinitely.
As a footnote, the status of the people of American Samoa is in a weird twilight zone currently. This Amendment would guarantee that all subjects of US power in the long term who are not required by treaty to be treated as noncitizens will be given full citizen status, retroactive to their birth assuming they were born in the territory and subject to normal US requirements for naturalization to subsequent immigrants or persons claiming extraterritorial status at the time the Amendment passes. This should settle the status of the Samoans!
----------
This then is the scheme I think we could think about Harry Truman proposing for approval as an Amendment sometime between 1946 and the Fall of China to Mao in 1949. 1947-48 seems like a good time for it. Post-war idealism mixing with emerging Cold War polarization both put a burden of magnimanity on the USA, to clean up our act in terms of granting those subject to our power on a permanent basis full citizenship and a fair share in the government that administers them, per our high flown principles. Truman seems like the man who could advocate for it and sell it to the state governments.
Now Truman had his own problems to be sure, and if the process is not complete before KMT China collapses, given Macao's situation it might backfire.
However observe that he did manage to get Puerto Rico's status...if not clarified really, then apparently so to the apparent near satisfaction of many Puerto Ricans at the time. DC was granted special rights in electing the President though little to Congress and none to Senate in the 1960s.
If the proposal falls through in the 1940s, I suspect that the 1960s would be an opportune time for it to be revived and put through in lieu of the more limited DC Electoral Vote and autonomy package of OTL. By the mid-60s liberal ascendency, US Cold War obligations would be all the stronger and the issues of racial civil rights would put all these diverse overseas peoples on the agenda.
With Macao, Timor and Goa established as Commonwealths with state-equivalent Congressional representation and Presidential voting rights, I daresay the question of their being alienated from the USA would be answered with a resounding "no." The USA would thus have permanent Sun Never Sets global presence to this day, and I doubt any of these entities would ever seek to secede and US power would have to plummet to a very low level indeed for any foreign power, however strong regionally or even globally, to seize them.