I think Putin is a suicidal person and will not hesitate to make an all-out war if ever the United States does something that can trigger Putin's emotions. It is mainly the reason why the US is very careful right now with its actions. However, we cannot really say what they are thinking because they continue to slap Russia's butt and then point their finger at Ukraine.

Tho, if US is just committed in Helping then I think they can not just end the war in Ukraine but I think it can end most of the countries