Your entire argument ignores the fact that Russia annexed Crimea in 2014. You're saying that NATO was stronger before Trump, and yet they (and the US in general) let Russia waltz in, and annex Ukraine and that was that?
How do you account for that fact in your worldview?
2014 should have been a wakeup call. 2014 was Putin dipping his toe into the water to see how the world would respond to an invasion, and IMO it wasn't harsh enough. But I don't think this had given Putin enough confidence to conduct the full-on invasion that he is right now. Then 2016 happened. Before 2016 Republicans were still staunchly very anti-Russia, as had been their traditional Cold-War position. Communism and authoritarianism: bad; Capitalism and democracy: good. That was the Republican party position in 2016. Not after Trump's nomination. At that point they turned from an anti-Russia party to the "Russia isn't all that bad, let's be friends with them" party. They removed military support for Ukraine from their party agenda at Trump's behest, at a time when his campaign manager and family was secretly meeting with Russians in his home. 2016-2020 was 4 years of the American right explicitly signaling to Putin that they would rather be aligned with him than European democracies, especially and in particular Ukraine.
To summarize my entire argument, it's that because of his own personal ambitions, Trump attempted to realign America with an axis of global dictators rather than our traditional democratic allies in Europe, and in doing so severely weakened NATO's standing because America as the largest economic and military power in the world is the key to that alliance.
If Putin invaded Ukraine while Trump was in office he would have forced the American political establishment to unite against him. It's far better for him now that there were 4 years of Republicans wearing "Better Russian than Democrat" shirts.
Think about how far Republicans have come on this issue. They used to be the party of the red scare, now they're the party of "Putin is a savvy genius". Amazing what a propaganda victory that is for Putin.