If Trump was President Russia wouldn't be invading Ukraine at all
Explain
Trump managed to go through an entire term with no new wars and no Russian expansion. The issues in Ukraine during the Obama years didn't go away.
Biden is senile, Harris is incompetent, and Putin is an "Intel Guy" that knows it. He's exploiting these factors. Trump was a strong President in that he was not afraid to take unconventional risks for peace and other leaders understood that. They also understood that Trump would not draw red lines he wasn't willing to cross.
Trump was also unencumbered by "what the rest of the world thinks". Most of that means concern for the multinational corporations, etc. Trump was, truly, American First, and that very fact was a deterrant. Putin is Russia First; he understands that.