As a number of pundits have pointed out, the new South Carolina TV ad from the Dem group Priorities USA slamming Mitt Romney over the Paul Ryan plan is airing unusually early in the cycle.

There’s a reason for this, and it’s not about Mitt Romney, even though he’s the target of the ad. Rather, it’s all about doing everything possible to ensure that Medicare is central to framing the Presidential race at the outset — by getting all the GOP candidates to talk about it.

Dems are airing this ad so early because Newt Gingrich’s condemnation of Paul Ryan’s Medicare proposals — and the ferocious backlash it triggered from Republicans — have presented a unique opportunity that Dems think they must exploit right now.

On a conference call with reporters just now, Paul Begala, one of the founders of Priorities USA, spelled out the thinking.

“It is very rare that a dominant issue emerges in a presidential race, but it has,” Begala said. “We believe Medicare will be a dominant issue.”

What Begala means is that Dems will do everything they can think of to make it so.

And so Begala seized on the Ryan plan to try to pit Romney against Jon Huntsman, because the two men are seen as vying for similar spaces in the field. Begala pointed out that Romney has not taken a position on the Romney plan, while Huntsman now has. “I would’ve voted for it,” Huntsman said on ABC News this morning. “Including the Medicare provisions.”

On the call, Begala said the new ad is designed to force Romney to take a position.

“Huntsman was asked a direct question about the Ryan plan — and unlike Mitt Romney, he gave a direct answer,” Begala continued. “I don’t agree with him, but at least he took a stand. It’s amazing that Mitt Romney, who’s clearly running hardest for the presidency, has not taken a position on this.”

So who does Romney side with: Huntsman, who supports Ryancare, or Gingrich, who has denounced the plan as radical? That’s the question the ad is designed to get reporters to ask Romney when he visits South Carolina tomorrow.

In other words, Obama’s allies are going to try to frame the 2012 race around Medicare at the outset by forcing Republicans to talk about it as much as possible.