The possibility that Republicans will recapture the Senate in 2014 lurks in the background of almost every story about American politics. The positive news about the Affordable Care Act is inextricably linked to the question of whether a Congress under complete GOP control would reopen its books. Many liberals are increasingly concerned about the possibility that Supreme Court Justice Ruth Bader Ginsburg will only be moved to retire after Democrats have lost a good measure of control over who will replace her. President Obama would probably have to veto a bunch of bills. Republicans would double their oversight capabilities.

And so on.

None of these scenarios is good for Democrats, and there's no sense in anyone convincing themselves that a GOP Senate takeover would be a wash for their party or the president.

But if you believe, as I do, that the most important meta-story in American politics today is the Republican Party's ongoing and increasingly bloody factional struggle for identity, a GOP Senate takeover would confront the party with new and fascinating internal challenges. With Senate Majority Leader Harry Reid sidelined, it would set the party up to do unencumbered battle with Obama, and deny him the opportunity to spend his last two years in office shaping his own legacy.

No doubt Obama wants to avoid that.