Democrats fall in love. Republicans fall in line.
Other way around. If republicans always fell in line then both Romney and McCain would have been elected president and Trump would have probably won the popular vote
Romney and McCain losing proves my point. Obama is a charismatic candidate that the base and independents fell in love with. When Democrats put up uninspiring candidates they lose. Trump's inexprence and instability could have been enough to reverse this phenomena with the Dems but Hillary's hubris and unpopularity were enough to give Trump the win. He wouldn't have won without hesitant Republicans pulling the lever for him.
He certainly would have lost as a Democrat with his high unfavorables. Constantly critiquing the first black president by questioning his legitimacy as president and being hostile to many progressive causes would have caused people to stay home. When turnout is down that is typically a Republican win.