Of course the U.S. should put its interest first, but it isn't a zero sum game. Helping other countries does not mean we are not helping ourselves. The U.S.A. is in a much better place when it doesn't have to fight a world war every 25 years.

I wish I could find it, but I recently read a piece suggesting that Trump's foreign and economic policy is shaped by a rejection of the idea that a deal could ever not be a zero sum game. IOW, in every deal, in every arrangement, there's a winner and a loser. If the other side is happy with the deal, it has to mean that your side is getting screwed somehow.

Not sure if I 100% agree with that, but it would explain some of his more puzzling policies - like starting a trade war with Canada. Canada obviously benefits by having a stable and peaceful, barrier-free relationship with the U.S. - but so too does the U.S. benefit by having one of the longest national borders on earth be with a close and tight ally that's deeply interconnected with our economy, rather than a more contentious boundary. But if you believe that if Canada's benefiting, the U.S. must be being treated "unfairly" (one word Trump uses to describe how they treat us)...well, it makes more sense.

As for Ukraine, the U.S. benefits not just from a stable and peaceful Europe specifically, but from a world governed by principles of collective security where the other major powers (and all the nuclear powers) face powerful disincentives to invade their neighbors. We benefit from the general rule ("There's a major price to pay if you invade a tiny neighbor"), even if we might pay a cost in any specific instance of defending that rule ("It costs the U.S. a lot to provide arms to Ukraine to defend itself"). I think Trump doesn't believe that the benefits of the general rule outweigh the costs of supporting it.