I'm gonna have to disagree. In the post-Cold War era, I think we've established international hegemony at the expense of a crippled and politically-impotent Russia, sweeping aside one former Soviet client regime after another. Putin is merely trying to stop the rot. Basically, we've pressed our bets for over a quarter-century after the Soviet empire crumbled. It remains to be seen whether the Russians will finally put their foot down and say the equivalent of "this far, but no further". One way of doing so would be for the Russians to take over Syria's air defenses, with S-400's based there, daring the US to bomb Russian personnel based in Syria and risking significant aircraft and personnel losses. If Putin decided to take this really seriously, Russia could sign a mutual defense treaty with Syria, making any attack on Syria an attack on Russia. I think the difficulty any president would have with Russia today is that Russia has been pushed around to the point that there is broad public support in Russia for ending this seemingly relentless series of retreats.