Which doesn't make sense with how an isolationist US would develop. The whole theme of US isolationism was "Europe does what it does with wars and leaves us and the America's alone". Nothing about the US makes any real logical sense here. The moment it even whiffed Mexico having a nuke program it should've done whatever it could've to stop it as that's an actual threat to national security, up to and including waging another war against them if needed.
Then there's the whole no space program thing which makes no sense at all. Like I said earlier Syria of all nations started one in 2014 AKA in the middle of the civil war they're currently undergoing.
Look, I don't particularly want to get into this because this is clearly something we'll have to agree to disagree on. As
@sarahz has observed, the Monro Doctrine was only ever effective in the 19th century if and when the Royal Navy continued to enforce it and that basic situation is continued TTL into the 20th century. Also, it was only the Roosevelt Corollary which asserted the US's rights to make unilateral interventions in other American countries even in the absence of European intervention - before that it was a basically anti-colonial doctrine. As I've discussed before, the US remains TTL much as it was in the OTL 19th century: an enormous economy but one which primarily existed to be a site for European emigration and a capital market for British investment. On the military front, the TTL US armed forces are hardly insignificant but they're much smaller than their OTL equivalent.
To take issue with your insistence about the Mexican nuclear programme and the space programme.
On Mexico, if you're the OTL US you're faced with a neighbour that has just unveiled a nuclear weapon. Your plan is to launch a land invasion of that country? My answer to that is "okay..." but I respectfully submit that there are at least some other reasonable responses to that.
On the space programme, while it's interesting that OTL Syria has developed a space programme in the past decade, I have to say that, while I haven't exactly crunched the numbers, I suspect that more countries have not begun space programmes in that period. Certainly not in the 1960s, which is the time period the questioner was referring to.