When the electoral college votes, Donald Trump will almost certainly receive a majority, although there is now a discussion of whether or not electors should break from the voters and do as Hamilton suggested in Federalist 68-- not give the presidency to an idiot psychopathic child who is unfit for office. A few points:
1) Trump is manifestly unfit for office. They still won't stop him. Remember the Republican nomination contest? Remember the lead-up to the convention? Think of all of the times that Republicans refused to do anything to stop him. You think they'll do anything now when it would be even more dangerous to democracy?
2) Legitimacy is as it is perceived. Trump won. He did it with a big assist from James Comey, a little bit of help from Putin (although I'm more skeptical that the hacks did much), and a hell of a lot of luck, but he won. To steal the election from him would be perceived as illegitimate, and tear down the basis of the electoral system. What are you willing to lose to stop Trump? Of course, the question isn't, "what are you willing to lose," but, "what are the electors willing to lose," and whether or not they think they need to lose anything...
3) No, the popular vote doesn't matter. Do I really have to keep on about this? There is no such thing as "the popular vote". Stop whining about it. Stop looking at the fake number. It doesn't exist. It is like the "score" in a game of chess. There are no points in chess. There is only checkmate or stalemate. (Or time running out, or you can limit the number of moves, or fine, fuck off, you get the point).
4) Even if enough electors defected in the EC to deny Trump a majority, it just goes to the House of Representatives, and they give the presidency to Trump.