If John McCain (or Huckster) is the Republican nominee, why would anyone, other than GOP loyalists, vote Republican? To paraphrase Harry Truman, if McCain (or Huckster) is the nominee, there won't be a dime's difference between the two parties. Given that, why not vote for the real deal in Hillary or Obama? McCain is an impostor. (Related: Michelle Malkin asks if the GOP is lost.)
Ronald Reagan won because he was sooooooo different from the Democrats that conservative Democrats and independents exercised the freedom of political choice and crossed over to our side. Reagan won because he was a conservative. Gerald Ford, George Bush 41, and Bob Dole lost because they offered no real choice. And if the two candidates are close, vote for the one who's in step with his own party.
The "Big Tent" Republicans were told to adopt in 1988 turns out to be nothing but a concentration camp for liberalism's Final Solution of the conservative problem.