Many countries in europe needed a wakeup call to spend more on defence, though Trump failed at that. That didn't change before ukraine, all Trump did was remind european leaders that the USA is not a trustworthy ally
hmm, Biden for example? I mean, if you want to be an isolationist power then this point doesn't work, but it's also in the american interest to be a global power with influence all over the globe. Trump seems among other thing willing to end support for ukraine for example, but then you're literally just shooting yourself in the foot before most of that money is going to modernizing the US military, whilst sending the stuff being replaced to someone fighting a country whose publicly stated goal is to destroy your global possition.
The US budget is already famous for running at a deficit. US gas prices are also already not that high all things considered, but ok. I'd argue the people who really need more money, like those living in the rust belt would be much better off if he invested in getting them jobs new sources of income though.
The medical lobby is big over there, and once Trump elected he has no vested interest in remaining popular. How a second generation billionare managed to convince the middle class that he's "their guy" is honestly amazing in of itself though. He put america first in a sense, but in an isolationist one. Historically that hasn't been the best long term play for the US
Don't forget that something like half the money "spent on ukraine" is actually spent on buying things for the US military, so the US military can then send 30, 40+ year old equipment to ukraine. Equipment that is otherwise not benefiting the US, and mainly geared towards fighting a land war, for which the need will be reduced if russia isn't a threat anymore. It also helps deter china and other authoritarian powers from possibly making any bold moves.