Rubio may very well be the nominee, but the general election is a whole different battleground. The Republicans are making a huge mistake by putting all of their eggs in Marcobot.
It's not just the Republicans covering for him though, it's the media. If he has a bad week on the campaign trail, a gaffe, or a poor debate? Just throw out more email stories or other Hillary faux scandals, or discuss how he's so much more "likable" despite his mishaps.
Or god forbid if Sanders is the nominee, just talk about how he's an f'ing SOCIALIST, and whatever little amazing Marco did can't compare to that godforsaken evil. And before Bernie's bots start quoting polls, you'll see how toxic Bernie embracing socialism really becomes after a full scale media and GOP assault.