Republican McCain ran against Obama as the nation was ending the era of another Republican President, George W Bush, during which we experienced what became known as the Great Recession, the worst economic times since the Great Depression. Romney ran against an incumbent who even today (outside of places such as CAF of course) maintains a reasonable popularity.
It has been very difficult though for awhile now for 1 party to win 3 straight WH terms. Only once since 1948 has it occurred when Republicans Reagan and his VP George HW Bush did so in 1980, 1984, 1988. So because of this fact, I’m going to have to differ just a bit with my friend, Little Sheep here.

I was never quick to rule out the chances of one of the other candidates beating HRC.
I agree I’m not sure Jeb Bush could have. Because this yr might still have been too close to his brother’s failed Presidency. And Cruz might be too far out there on the extreme right for a general election electorate. Same with someone like a Ben Carson. But someone more or who at least comes across as more moderate like a Kasich, I think would have given the GOP a reasonable betting chance this go-round. But it would have taken a unified GOP.