Russia would not use nuclear weapons against the US or NATO if we pushed Russian forces out of most of Ukraine but didn't retake some of the seperatist regions or Crimea. That would be more likely if we moved across the Russian border. But who knows.
The smart move, if wearing my general's hat, would be to leave Ukraine to tie up the Russians and move across Belarus from Poland and cut off the Russian supply lines there and into northern Ukraine. If the bulk of Russian forces move deep into Ukraine that would leave them with no line of retreat or additional support. You'd see 100,000 strong invasion force surrender in a matter of days.
Of course, no idea, what we have in Poland that could accomplish this. Again, people saying this is crazy because Russia has nukes, guess what, so do we. Russia will not respond with nuclear weapons over a military defeat in Ukraine. They didn't nuke Chechnya or Afghanistan. The US didn't nuke North Korea. It's just not going to happen even when military set backs are faced.
It's a deterrent that once you use, it, game over. Having your forces pushed out of or surrender in the Ukraine is not game over territory.