Quinnipiac's poll of today has Trump at 27, Rubio at 17 and Carson at 16. Not only does Rubio have a shot, it's increasingly looking like Trump or him, and if they manage to narrow things down to two fast enough, I think we all agree the establishment candidate will take it in the end. For all that Trump has been leading for months and keeps defying the expectations of his impending fall, I think the fundamental strategic point is the same it always was: he's not going to win unless the establishment and the evangelicals remain deeply split all the way to the convention.
Trump or Carson can't compete in the general election. Bush, Christie or Kasich could compete, but they don't look like they can make it there. Rubio could do both - I would still expect Clinton to win in the end, but he'd make it close and all sorts of things could give him the edge. In any case, a close race in the presidential means no Senate majority for the Dems, no House, and if they don't take them in 2016, they won't in 2018 either.
not one candidate can compete in the general election. the dems only hope for taking back the Senate is this year, otherwise they will not get another chance until 2020. thanks to gerrymandering, the dems have zero chance to pick up seats in the house until 2020, and we'll probably have yet another federal election in which they win more votes than republicans but republicans increase their seats.
the biggest problem rubio has -- besides his absenteeism from his current job -- is that he has a history of siding with his party on substantial issues, and most of those issues are detrimental to a lot of the people who will be voting next year. any of the republican candidates is guaranteed at least 110 electoral votes, because those are pretty much guaranteed to the republicans no matter who the candidate is. the handful of "leans republican" states may add up to 50-70 more, but the presidential race is the dems to lose this year and neither Hillary nor Bernie Sanders is likely to screw this one up.
"That's the trouble with political jokes in this country... they get elected!" -- Dave Lippman