The ISW has run a piece named "The high price of losing Ukraine:
Military-Strategic and Financial Implications of Russian Victory", which describes that if Ukraine would loose there is much more at stake for the USA than many people do comprehend.
According to the ISW it would mean a strengthened and better Russian army, which would be an increased threat to NATO. NATO would be unable to defend itself with the forces currently stationed in Europe. As consequence the states would have to deploy a good portion of its fleet of stealth aircraft permanently in Europe as well increase its troop presence again, which then would be missing in Asia/Pacific, to China, meaning it could decrease America's ability to respond effectively to Chinese aggression to Taiwan.
So in short its better and much cheaper in their opinion to support Ukraine than to let Russia win.
The United States has a much higher stake in Russia's war on Ukraine than most people think. A Russian conquest of all of Ukraine is by no means impossible if the United States cuts off all military assistance and Europe follows suit. Such an outcome would bring a battered but triumphant Russian...
www.understandingwar.org