If Vladimir Putin invades Poland, I’ll eat my hat. It’s not going to happen.
Even so, American ground troops are being deployed there as a response to Russia’s invasion of Ukraine and annexation of Crimea. This is the West telling him STOP. He’s not going to invade a European Union or NATO state either way, but we’d end up sending a crazy-weak signal if all we did was collectively shrug.
Ukraine still isn’t in NATO, however, and probably never will be, so it’s still vulnerable. Putin can slice it and dice it all over again. The US won’t physically stop him for the same reason he won’t invade Poland. Nobody wants to blow up the world, especially not over this.