I'm not with Trump's framing on this issue at all.
But the way it happens is that Putin eventually takes Ukraine, and moves on to Poland. He calls Europe's bluff on NATO and sees what happens. Does Western Europe have the will or the wealth or the wherewithal to fight? Have you seen the state of Europe?
Honestly, look at this:
JUST 17 per cent of British people would “willingly” fight for the UK in a war, a new poll has found ...
www.thenational.scot
And the UK are historically the baddasses of Western Europe. Europe is in steep decline, economically stagnant, culturally irrelevant. They still have trouble keeping the lights on without Russian fossil fuels.
After years of war and promises to change course, the continent maintains ties to Russian fossil fuels.
foreignpolicy.com
What does it mean for the Western world to be against you, if they are in fiscal crisis, their militaries are shit, their populations have no patriotism, and they won't really fight? Many of you still have WAY too high an opinion of Western Europe at the moment and aren't paying any attention to what's happening there.
If Putin finally conquers Ukraine fully, he may well decide that Europe doesn't have the will to stop him.