Peace Negotiations is the only way this stops. Withdrawal comes after that.
Thinking it happens the other way round is naive.
Negotiatons requires both sides, usually involves concessions from both sides, and Ukraine needs its overlords say so. Murderica & Co will be required to compromise or give up something, and that won't happen. At least not until the 'latest' weapons market/testing ground has satiated its corporations.
So America has just as much power to stop this. It won't. This is such a great opportunity. Market/test weapons, fleece EU, bleed Russia, opportunity for change/overthrow Russia's leadership/structure leads to the ultimate goal, getting that sweet resource trove it(Russia) owns divied up to its corporations under the guise of 'FREEDOM'