Who else is going to stop them?
The repubs have shown a willingness to put team first, no matter what. That's how they won in 2016 and if the dems continue playing games, they'll win again this year. Every repub will stay in lock-step with the party and virtually every registered repub will dutifully vote for Trump, meanwhile the dems continue to balkanize the party.
Like it or not party politics are what we have now - if the dems cannot come together and rally behind whomever wins the nomination (and not destroy / undermine each candidate int he process), we're getting four more years of Trump.