I am somewhat conflicted about Putin's invasion of the Ukraine. I think it is wanton piracy, the stealing of another nation's sovereignty through armed conquest, and it is immoral and evil.
So what do we do about it?
The wisest answer: nothing. Well, except for denouncing Russia in the United Nations and in speeches and in print, all the usual political and diplomatic channels that accomplish nothing much. However, we should not commit troops, or invade the Ukraine, or fight Russia with arms.
Why? Because the Ukraine and Russia have a shared history, though not an honorable one, and the Ukraine is within the Russian sphere of influence. We have nothing to gain by intervening in the Russian-Ukrainian war. We have no strategic interest in doing so, and we should not do so.