Ukraine has to be endlessly frustrating for Biden, because, due mostly to geography, Putin never has to give up the initiative. He can squeeze, relax, or invade any time he likes. We can only react and attempt to deter.
If we had an autocratic political system, things would be different. Biden could send the Sixth Fleet to the shores of Syria and threaten to obliterate Assad and all of the Russians’ investments if anything happens in Ukraine. The pressure could be increased and relaxed in proportion to the events at the Ukrainian border. Putin would no longer be able to dictate the agenda.
This won’t happen, of course, because Biden isn’t a dictator, and Congress and the American people wouldn’t stand for it. In a world completely controlled by realpolitik, however, it would.