Let's assume that if Obama loses in 2012, or has a mediocre record when he finishes in 2016, that many Democrats begin to believe it was because he was not liberal enough. This is sort of similar to the Tea Party movement after George Bush. Then, many people on the left start to change the Democratic party into a Social Democratic party, eventually changing the national party.
Now let's assume that the Republican Party becomes even more libertarian. Less religious, and although still a pro-life party, still open to voters and candidates who may be pro-choice. (Similar to the current Democratic Party's position on gay marriage)
This is what I came up with:
Social Dem: 243
Libertarian: 233
Toss-up: 62