A big part of the Republican split, in my opinion, has to do with the fact that Moderates don't know how to save face after voting for Obama. As the Obama administration begins to slip in popularity, and as Obama's agenda is being revealed for what it is -- progressive and bad for the country -- Moderates are put in an embarrassing position. To admit they are wrong and the conservative base is right is too difficult to even contemplate, so the Moderates have find a way to maintain the validity of their criticisms against the conservative while also finding a way out from under the Obama wet blanket.
The Moderates have to justify their previous support for Obama, while at the same time distancing themselves from the coming political fall-out. This is not an easy task. The Moderates can't just admit they were wrong about Obama and the conservative base was right, because that would be tantamount to admitting defeat in the war for control of the Republican Party -- plus, the Moderates still think the conservative base is wrong and that they will destroy any chance to win in 2012.
The Moderates, in order to have it both ways, will have to convince independents that Obama turned out to be something other than they expected, but the orginal impulse to vote for Obama was legitimate, because moderation is still the way to go to build that Big Tent and win an election. I have a feeling that the Democrats are going to push their agenda to the point of implosion, and the Moderates will have painted themselves in another corner by continuing to call for moderation and compromise. When independents look at the state of the Democrat Party and realize something totally opposite needs to take its place, moderate statism and compromise are going to be a tough sell, especially when the conservatives have been resisting the progressive agenda from the beginning. The Republican primaries in 2012 are going to be a good show.