Just because Trump is honest, and calls Putin what he is, which is intelligent, and describes his moves as brilliant (which they may or may not be, depending on one's opinion) does not mean he's Putin's buddy. Why do people mistake honesty and having a keen grasp of the obvious in terms of assessing peoples' personalities, for admiration? I'll tell you why I think why; it's because the media tells them that's what they believe. You strike me as being smarter than believing something the media wants you to believe, so I'm not sure why you've fallen for it.
The reason Putin didn't try any shit on Trump's watch is because he knows Trump is strong, and he respects that strength. (and btw, respecting that strength does not mean he wants to shower with him, okay?) So the reason Putin started this up on Biden's watch should be obvious, but I'll specify anyway, it's because Biden is the opposite of Trump, no mean tweets and all.