Take economic sanctions against Russian Federation, with asset freeze of Russians and Russian companies in US.

With heightening risks of WWIII such a preventative measure would, force Russian side, to start peace talk, as well as pressure Russian president to honor territorial integrity of Ukraine. Only by economic power of US and EU, Russian president would stop his militarized rating boosting, as well as exercising his campaign aimed at destabilizing ethical tension both in Ukraine and Russia.
Please consider that in intertwine and global world we live in now, money and financial strength is more powerful than military warfare. A relatively small price we pay now, by those sanctions is much smaller then the bill we will get in case of escalation of military conflict.
God Bless America.