1) I don't think it's such a slam-dunk that McKinley will suffer certain defeat in '00 if he takes a pacifist stand. If he does the main reason will be that his party, particularly the pro-corporate wing of it that did so much to help him win election in the first place, is hawkish. But the American people as a whole are more balanced. I daresay one reason the war was a political winner in the USA was that quite a lot of Southern Democrats were probably for it--most of those people still wouldn't vote for a Republican President though, so he's not going to lose any reelection votes in that column. Having accounted (with no numbers, no statistics, no evidence but a hand-waving gut feeling to be sure
) for a big part of the hawkish sentiment with lots of Southerners who wouldn't vote for McKinley anyway, that leaves the balance of Northern opinion to sort out. Again I've got nothing but gut-feeling impressions, but I rather think that the ideology that the USA ought not to entangle itself in foreign wars unnecessarily was still fairly strong and cut across partisan lines. The Republican Party was I suppose by this point largely purged of somewhat leftist types who had already defected to a succession of split-off parties and eventually the People's Party--leaving behind a whole lot of moderates alongside the gung-ho robber-barons and their admirers who still felt that the party of Lincoln stood for a kind of Victorian moralism; these loyalists, along to be sure with the Robber Barons and their acolytes, delivered the Presidency to Republicans every time between 1868 and 1912 except for Grover Cleveland's two non-consecutive terms.
So it all boils down to the question of just how deep and wide the war-hawk sentiment went across the spectrum of non-Southern voters (since the Solid South would vote for the Democrat in any case). My guess is that it was rather close to an even split--in fact, a split between a minority of rabid hawks on one side and another minority of pacifists on the other, with the clear majority pretty much indifferent. If Congress and the President (in that order, the Presidency was much less powerful than we'd assume today) delivered a declaration of war--well, then, that indifferent majority would back it, and in retrospect most of them declare themselves hawks with the rest. Glory and the conquest of non-Anglo, non-white people certainly had currency! If I am to believe Robert Heinlein's last novel (which, to be sure, I tossed across the room and stopped reading at this point) middle Americans honestly felt Spain might be some kind of threat and was the aggressor. But that was on the say-so of their leaders; if their representative leadership did not come to that consensus they'd probably shrug off the possible glory and get on with their lives without worrying any more about Spanish ruled islands overseas.
So--it isn't clear to me McKinley even loses net support in Congress come the '98 elections. Some politicians would suffer for not voting for war, but others might benefit--I'd guess the outcome is a wash, and that McKinley might not steamroller Bryan by quite as much in '00 but would win anyway.
Unless the Republican convention deposes him in favor of someone more malleable to corporate interests that is, which is his worst point of vulnerability. But if he really wants to stay in office, he might well be able to outmaneuver the money wing of the party--surely not without winning over some of them, I should say then he wins over the non-hawk contingent of the money wing instead.
American imperialism worked out pretty well from its advocates' point of view, to be sure, so in retrospect we can discern a solid block of very influential opinion we might guess would fight for it, and punish any politician they could who wouldn't back it. But I think that before the fact of success, not a few would consider the possibility that it might backfire--as martin76 and others have pointed out, it sort of did backfire OTL--he doesn't even touch on the drawn-out costs of the US trying to maintain supremacy in the Philippines. Not to an extent that the domestic issues led to a massive backlash, since the whole enterprise was done on a basis of volunteer soldiers and sailors and a modest expenditure of money, whereas--again
after the fact--the US appeared at least to profit immensely. I'm not sure what a hard-headed and even-handed economic analysis would show, for the nation as a whole--but the nation as a whole doesn't effectively exist unless its democracy is very robust and very critical; a good number of rich people got richer one way or another, and prestige-wise the USA was in the global imperial game as an "honorable" contender but at low cost, with stations (sparsely!) spotted around the globe, or a good part of an arc anyway, no longer a merely regional power.
But with the butcher's bill not known in advance, and the likelihood American intrusion into the Caribbean and Pacific on this scale might backfire, involving us in conflict with a real imperial power also up in the air, I can see a lot of these same beneficiaries of the OTL aggression going along with a softer line; therefore McKinley, as a President presiding over prosperity
and peace might not be the dead duck at the Republican '00 convention (two years after the crisis after all) people are assuming here.
Will the Imperialists still be gnashing their teeth, trying to get hold of the US saber and rattle it, if they miss this golden opportunity? Well, presumably the US not jumping in to gobble up the Spanish insular empire butterflies things and other crises might arise.
2) Again though I don't think it's so clear-cut that if the USA fails to mobilize to conquer and impose a conqueror's peace in the Caribbean and the Philippines, that therefore some other imperial power will necessarily move in to seize them instead. How well the Spanish could do at continuing to hold them I leave to others who claim to know more than I do about Spain's situation--but my feeling is, their imperial grasp was indeed fatally weak. My bet would be on the insurgent native freedom fighters, in both hemispheres.
Having finally driven the Spanish crown from their islands, would the Cubans, Puerto Ricans (hey, did PR even have an insurgency?) and Filipinos necessarily see the Japanese or Germans come swooping in? I can see at least two Great Powers who would tend to interfere--Great Britain--and the USA!
The Americans might win by soft power what they chose not to seize by hard power. McKinley, or any alternative President, would still have the expansionists lobbying him, and I can't identify any US faction who would actually favor Spain. McKinley refraining from a declaration of war does not relieve Spain of all Yankee pressure; the old American tradition of filibustering might live on longer, with blockade runners and even volunteer fighters mixing up in the domestic insurrections--Madrid might call foul but they are hardly going to risk a declaration of war of their own. The Monroe Doctrine is a factor in the Caribbean; US policy frowns on formal holdings by European powers--not too deeply when they are stable, but if a republican insurrection is successful, the USA opposes a third party vulture swooping in and favors the new republic, however weak and shaky it is. And US private interests will show up at once, to offer their "services."
Our main rival in that game of indirect rule being none other than Great Britain, the power whose ambassador proposed the "Monroe" Doctrine to that President's Secretary of State in the first place. Under the umbrella of Yankee cries of "hands off the Americas!" (quite impotent in the early 19th century when the Doctrine was first uttered) the British crown was quite happy to keep up the appearance of a hemisphere of free republics while having such strong informal influence over the regimes that they favored that they reaped the profits of empire. The American position served as diplomatic cover for their own interest in informal, indirect rule and blocked other European powers from trying to move in by main force.
If then the Yankees failed to give the new Cuban Republic adequate cover, the British would. De facto it would fall into one sphere or the other.
The Philippines are more speculative, but is it really clear that Japan could project enough power at this point to secure control of the islands against the organized will of that people's successful insurrection? Surely the Filipinos had no navy of their own to fight off Japanese landings--but they'd have options. They could call on the British for help, and negotiate a treaty with them. Or they could call on the Americans, who were hungrier than the British--but a treaty that gave the Yankees a port in Manila need not formally offer much more to attract that American base. And that I think would be sufficient to deter any attempts at casual, cheap conquest. It would lead to the Americans having an undue influence of course, but it isn't evident to me we'd necessarily then set out to formally conquer the archipelago.
If the Americans are not invited in, in gratitude for sympathetic services rendered during the rising, then the default is more British protectorate than the latter allowing the Germans to seize a base. Might they hand off the protectorate to the Japanese instead? Perhaps, but I don't think they would without Japan exercising leverage they didn't yet have. And probably not without finding a sufficient number of Filipino leaders who would assent to the idea, meaning Japan's interest in the Philippines would not be one of a conqueror but more like the one I imagined the Americans had--allied in partnership at least with a minority clique of locals, and with the Philippines remaining formally independent.
Even if it is Japan that wins on these terms, the outcome in the 20th century might be very different. Americans will have dropped the ball on imperial expansion into the Pacific big time. But we'd still probably have Samoa and Hawaii, so we'd be present--but perhaps not with the same hostile attitude to Japan. Japan would have preferential access to a region supplying tropical resources, possibly rubber plantations for instance, and so might not be as determined as they became during the Depression OTL to seize an empire in China, nor feel driven to attack other southeast Asian colonies. The experience of keeping an upper hand in the Philippines might educate the Japanese in how to win over Asian cooperation on a more voluntary, mutual benefit basis--and therefore Japan might indeed become a threat to the status quo, threatening Dutch, French, and British holdings--but doing so on the basis of alliance with local subversive independence factions. The Japanese might then clash with the European great powers, but would the USA be necessarily involved on their side, if our only actual holdings were a handful of distant islands in the middle of the Pacific?
In any case, even if Theodore Roosevelt's own career is sidetracked, I would think Progressive interests in the USA would be too strong to be simply butterflied away. Progressivism was basically an upper-class prophylactic against otherwise possibly rampant Populism. "Enlightened" reform from above might be needed to ward off wildcat radical democracy from below, as such reactionary figures as Bismarck in Germany understood; also reforms could work to make US industry more competitive and hence more profitable so it had allies of a less idealistic sort in US ruling circles. If this movement was somewhat disconnected from global imperialist ventures by McKinley's ATL neutralism, it probably would still remain entwined with Western Hemisphere assertions of hegemony. OTL it was TR who led the charge, securing US control of Panama, dismissing European gunboat debt collectors by asserting a Yankee mandate to perform that "service," etc. But I daresay if he were removed from such a position, other US leaders would take his place regarding our assertion of more control of the Americas.
One career that would be drastically butterflied by no Spanish-American War would be that of Smedley S. Butler, USMC. Indeed the Marines themselves owe much of their modern form to the post-war reforms. But I'd think that with adventurism remaining a thing in the Western Hemisphere, the Marines might still be reformed on OTL lines and it is even possible Butler would force his way in despite his family's disapproval. (In Butler's case though the OTL war did represent a unique opportunity for the hot-blooded youth, and even if he did enter a reformed Corps under his father's terms, as a college-graduate officer, his career would differ because he would lack the OTL experience of serving as an ordinary enlisted Marine).
It does seem likely that a USA that did not seize the moment and get itself a few subject colonies in the tropics in 1898 would differ somewhat, and in some respects clearly for the worse (such as, attempting to play a part in the ground war in Europe during the Great War). I'd think though than an inept initial performance on the part of a US expeditionary force would draw the Germans into a longer war--in which time the US forces would learn lessons belatedly and reform on the spot, and ultimately win. It's what we did during WWII after all.
On the whole it looks like a somewhat better world to me.
