[michaelt]

Theoretically, the US might hope to turn Ukraine into Russia's Iraq - never any decisive loss, just gradually bleeding soldiers and equipment for 20 years for little benefit, until they get bored and go home.

A conspiracy-minded person who thought America blew up the Nordstream pipelines to reduce Europe's dependence on Russian gas might see a similar benefit to prolonging the conflict.

[yks]

The US itself is in the state of being always a few years away from taken over by a crowd very sympathetic to the Putin's cause and Putin personally. Prolonging this conflict is therefore also quite risky to the current establishment or whatever you want to call the adherents of the post-WW2 world order.

[weard_beard]

The US is in the state of being always a few years away from taken over by any interest with money. When the money runs out, it is no longer a few years away.

See: Sam Bankman-Fried.

[yks]

That is true, but Russia in particular had practically unlimited money to buy off both the US elites and their opposition, due to the rich natural resources and lack of need to support the high standards of living for the Russian population. Only China has more resources but so far they haven't formed a powerful message US politicians can use to rally their constituents to pro-China causes.