The EU would have to make some very serious budgeting changes if they wanted to fill that void. A bunch of EU politicians would need to make the case for deep budget cuts, tax increases, war bonds, or some combination of those.
I just want to mention that EU has around €200 billion in frozen Russian assets. On top of that the various countries will contribute.
Even if it turned out that Trump has some backroom deal with Putin, and pushes hard for Ukraine to surrender - he'd be an absolute fool to not take that kind of money, and sell arms to European allies, and Ukraine.
That's money in the pocket for the US arms industry.
It's around 1 year worth of aid. Since the beginning of the invasion (February 2022) Ukraine has received approximately €400 billion in aid.
The silver lining is that the war costs much more to Russia - and that economic damage is accelerating as long as the sanctions are up. Russian interest rates being over 20% is a sign that things are starting to turn dire.
Whatever booming economy they're reporting, is a economy cannibalizing itself.
So, if Ukraine has the means to keep fighting, that will weaken Russia financially.
Why don't they? Isolationist USA is not ideal, but USA spending way more defending Ukraine than the combined EU is also stupid. Russia is literally knocking on their doorsteps, they should be the first to push back.
I really hope too. If Taiwan falls, what message does it send to Japan, South Korea, the Philippines? Are the US willing to lose their influence there and give a free pass to China?
I am most worried about East Asia, really hoping Taiwan survives the next 4 years.