America is not ready for a Socialist, Conservative turnout would be around 99%, moderate Democrats would sit out the election.
I'm pretty sure California, New York, and Maryland would vote for a pile of dog crap before they voted for ANY Republican president.
Also, don't most Republicans and otherwise right-leaners already see Obama as a socialist? They've certainly been screaming it from the rooftops for 6 years. I mean, it would hurt Sanders of course, but I think "the boy who cried wolf" effect will certainly kick in and make it less impactful than it otherwise would've been. Let's not forget that the base is calling people like Thad Cochran and Richard Lugar "socialists" these days.