While a Ron Paul ad on actual broadcast television (instead of just the Internets) is rare, it’s the message that has political observers talking.

It’s an attack on newly crowned front-runner Rick Santorum, whose emergence as the top conservative alternative to Mitt Romney isn’t sitting well with Paul, because, the advertisement argues, Santorum’s not a real fiscal conservative:

The ad is now running in Michigan, one of two states holding its primary next Tuesday, and the one that Michigan native Romney is desperately trying to hold on to (a new poll says Romney is clinging to a 32-30 percent lead, while others say Santorum is still leading).

“Ever Notice That Ron Paul’s Ads Seem To Help Romney?” asked Benjy Sarlin of Talking Points Memo, referring not just to this spot, but to Paul’s early Newt Gingrich attack ad “Serial Hypocrisy,” which helped stall the former Speaker of the House’s Iowa momentum. 

As Amy Gardner of the Washington Post has already noted, Romney and Paul have an unlikely bond, both personally and, perhaps, politically. Anthony Terrell of NBC News, who reported yesterday that’s he received anti-Santorum, pro-Romney opposition research from a senior Ron Paul campaign staffer, calls it “the emerging Mitt Romney/Ron Paul bro-mance.”

Last week, Richard Oppel Jr. of the New York Times (who’s based in Texas) also profiled the relationship. Oppel wrote:

In a Republican presidential contest known for its angry rivalries, the Romney-Paul relationship stands out for its behind-the-scenes civility. It is a friendship that, by Mr. Paul’s telling, Mr. Romney has worked to cultivate….

Mr. Paul volunteered that since his rivals were largely identical in policy substance, “when it comes down to those three, it’s probably going to be management style more than anything else.” According to one person close to the Paul campaign, it would be accurate to infer from that phrasing — “management style” — that Mr. Paul has a willingness to listen to overtures from Mr. Romney, who has been trying to sell himself to voters as a proven manager.

It remains to be seen whether that relationship will bear fruit come convention time, when Romney needs delegates and Paul wants to see his viewpoints (and his son, Kentucky Senator Rand Paul) represented. But with the Santorum television ad, it’s bearing some fruit now, and that’s likely to continue at tonight’s CNN debate in Mesa, Arizona, the first debate since the one on January 26 in Florida.

“This will be the first debate where Santorum is the main attraction,” former Republican National Committee political director Gentry Collins told CNN. “The attacks should come from all three other candidates.”

Dave Weigel at Slate is more specific:

Romney and Paul will share a debate stage with Santorum and Gingrich, both of whom have to attack Romney and don’t have any competitive interest in Paul. He’ll be busy; he’ll be Romney’s sole ally up there.

With Paul lagging in fourth place nationally–and still the only candidate who hasn’t won a state–it will be interesting to see if he gets enough air time to support Weigel’s theory, or if the networks will go back to treating him the way CBS did in November.