Tripwire forces can be withdrawn at the discretion of the nation that sent them. That doesn't give Ukraine its nukes back.
To preface, I'm approaching this from the perspective that the USA is hypothetically changing its mind rather than cynically deceiving Ukraine. So if Ukraine convinces the Clinton administration, and also two thirds of the Senate (required for treaty approval), that it's worth it to have American troops on the ground in Ukraine helping guard that country against invasion, I don't think it's really likely that a complete reversal will take place and troops are withdrawn etc. merely because Republicans gain the White House. It's much more likely that the close cooperation on the ground deepens ties. And besides, Bush was all about expanding NATO. Neoconservative interventionism may be discredited
now, but not in 1992 or 2002. So it would be pretty weird if he threw an Eastern European ally in the trash for no reason, especially when they were helping out with the war on terror if such still happens in this AU. (And they
would help, in order to stay glued to the USA as they are trying to do. It wouldn't cost too much.)
Or if, in the AU, the future-history warning of "neocons done goofed" is enough to discredit their ideology, surely the same public that found the future history so convincing would be convinced of the need to guard against the future corrupt violent regime in Russia?