This war probably would have been over very soon if Biden had approved Zelensky's plan for victory. Apparently, he did not.
Putin is now encouraged to renew his conquest of Ukraine.
The reason Biden refused Zelensky's plan is that a total Ukrainian victory would cause a total political collapse of Russia and/or WWIII. That's not what Biden wants.
U.S. analysts still believe that the Russian economy will eventually collapse, but the political system will transition in an orderly way - probably a military coup.
A total political collapse could trigger an invasion of Russia by any of its neighbors. Russia is surrounded by ancient enemies that would love to carve up Russia once and for all (ask
Litwin ).
NATO is a defensive alliance, but nothing could stop a subset of NATO countries along with China from forming another alliance to attack Russia.
Right now, the U.S & the U.K. are the only major military powers that have no interest in carving up Russia.