I figure 17. IMHO:
California, Hawaii, Oregon, Washington, Vermont, Maine, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Maryland, Delaware, Illinois, Minnesota, Michigan, Colorado.
Washington DC
He loses CO and MI IMHO.
I say Oregon and New Jersey will go Republican - I bet no more than 15, too. Oh, and I think Minnesota and New York are in play, so 13 is not unreasonable.