We never got to see David Perdue’s internal campaign strategy, but by now I think we know the gist of it:

“Michelle Nunn = Barack Obama”

Certainly, that was his one overriding message, the message that he drove home at every opportunity, from debates to TV advertising to public appearances. He adopted that as his mantra because he was told it works, and depending on last night’s results — results not available as I write this — those who whispered that advice in his ear may have been right. If the pollsters have nailed their turnout models, what had once been an almost even race in Georgia had begun to swing slowly back in Perdue’s direction in the last two weeks.

And it’s not just Georgia. Nationally, Democrats were trying to hold on to Senate seats in seven states that were won by Mitt Romney in 2012, including six states that Romney won in landslides of at least 14 percentage points. Given that favorable battlefield, Republicans have of course framed the campaign as yet another referendum on Obama, the final chance for the GOP base to vent its frustration against the president. He has been the issue, and the only issue.

If the races played out as the experts suggest, Republicans will now enjoy majorities in both the House and Senate, and with the likes of Tom Cotton of Arkansas and Jodi Ernst of Iowa in the Senate, the makeup of those majorities will be substantially more conservative and even more committed to warfare against Obama than they have been in the past. (That may be hard to believe, but it’s true.) They’ll want to turn partisan warfare up to 11 on the Tufnel scale, and I doubt that John Boehner and Mitch McConnell will have the authority within their caucuses to dial it back.

I’m curious, though: What happens to a party that has defined and united itself by ardent opposition to a political figure who will soon be leaving the scene? Because the truth is, Obama has been the most important person in Republican politics since Ronald Reagan; no one else comes close. In a perverse way, he is their leader, and I’m not sure what they’re going to do without him.

Yes, Bill Clinton performed a somewhat similar function for Republicans in the ’90s, as did George W. Bush for Democrats in the last third of his presidency. Hillary Clinton will be drafted into that role should she become the Democratic nominee in 2016. In politics, it’s always easier to define yourself by what you’re against rather than what you’re for, and that been true of both parties.

However, Obama’s case is something special and has been from the beginning. His looming presence as the GOP’s “bête noire” has allowed the party to paper over its own internal differences, to disguise its own lack of a policy agenda, and to postpone long-needed but painful adjustments to economic, cultural and demographic reality. He is the radioactive source of almost all of the energy that animates the GOP, and if Republicans do take control of the Senate on a platform that consists almost entirely of opposition to him, he is guaranteed to continue in that role for the next two years.

The problem is, that brand of politics has an expiration date, and it’s approaching pretty fast.