Whatever the merits of ACA, it is now something the Dems own. For decades I've watched Dems try to run away from things which have been surgically implanted on any politician with a D next to their name. It's always bizarre and pointless. You're the party of gay marriage, abortion, and Obamacare whether you like it or not, and it's better to convince your constituents that you're going to do good things for them than to try to convince them that you're not a real Democrat.
They can already vote for someone who isn't a real Democrat. He or she is called a Republican.