If we're looking at the contrasts between two stunningly bad candidates, I guess it's fair to say that Romney could look even worse than Santorum. But my guess is that, especially after the Dems are done with him, the only people Santorum would attract in the general would be the hardcore "anyone but Obama, literally" voters. Obama, or Obama and a rational Independent, get the rest.
I suppose Santorum could have a chance in the general if Obama and the Independent split the vote. That opens the door to some questions about electoral vote totals.
From what I've seen, you've been honest all along about the state of the GOP field, and the fact that Obama's chances are clearly increasing with the (slow) improvement of the economy.
My guess is that, unless something big goes south between now and November (and/or the GOP gets an actual candidate), Obama wins, and it won't be terribly close. The next question is the down-ballot voting.
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HIstorically, when a third party guy has cut into an incumbant's lead, it's usually because his own base has been has been disaffected. I think this was the case with John Anderson in 1980 and Ross Perot in 1992.
I think the breakdown will be about 52-48 in Obama's favor. I think he'll win, but he won't do as well as he did in 2008. For one thing, the young folks who came out for him in droves in 2008 will be disaffected.
Of course, Obama doesn't HAVE to do as well. He just has to do well enough. He can lose NC, VA, IN and FL, and still win the election.
Romney won't retake those states, but Santorum might. I think Santorum can also give him a run for his money in Rust Belt states where the recovery has been, how do I put this, lacking?
Now, downballot is a more interesting question.
The Senate is a lost cause for Obama. The Democrats are defending to many seats. The GOP only has two vulnerable seats- Nevada and Massachusetts. The Democrats will definitely lose ND and NE's open seats. So best case scenario, everything blowing in the right direction, the best they can hope for is to maintain teh status quo. They also have 6 seats that are tossups- FL, MI, MO, MT, VA and WI. The last two are open seats.
On the house side, the bigger issue is going to be dedistricting more than any surge. I think any coattails Obama has will be nullified by the Gerrymandering that was done.
Now, that said, historically, when incumbants have been returned, they don't really have long coattails. Bush won in 2004, but he only gained 4 seats in the Senate and 4 in the house. Clinton lost two senate seats and gained only 9 house seats. Reagan won 49 states and the biggest landslide since FDR, but only gained 16 house seats and actually lost a net seat in the Senate.
So it's very likely that Obama, if re-elected, will not have much joy in Congress. It's more likely that the voters will return Obama and a GOP Congress to keep an eye on him.
And in 2014, Obama is kind of screwed, because all those Senate Seats he picked up in 2008 will be up for re-election. He's a lame duck in 2015.