I’ve long wondered why more Republican presidential candidates don’t talk about Mitt Romney’s record on jobs. It seems like a campaign-killing issue — in part because his record is so atrocious, and in part because Romney pretends it’s his signature issue — but most of the GOP field has held its fire.

It’s possible, though, that Romney’s rivals have held back because they’re waiting for the race to heat up — and it’s getting to be about that time.

At a campaign event in South Carolina over the weekend, for example, Rick Perry told voters at a town-hall meeting, “There’s going to be some that get up and say, ‘Well, I created jobs.’ And that’s true. One in particular that’s created jobs all over the world. But while he was the governor of Massachusetts he didn’t create very many.”

Jon Huntsman is proving to be even more aggressive on this.

Jon Huntsman just removed any doubt about who he’ll be gunning for in the POLITICO/NBC debate tomorrow night.

The former Utah governor’s campaign has produced a video — “#1 vs. #47” is the title — contrasting Huntsman’s jobs record with Mitt Romney’s. Under Huntsman, Utah was first in the nation in job growth, Under Romney, Massachusetts was 47th.

There’s no mention of Romney by name, but there’s also no question which candidate the video is referring to when it says there’s a Republican with “one of the saddest records” in the country and “sadly similar” to Barack Obama on jobs.

“Numbers never lie,” the ad says. “As the conservative governor of Utah, Jon Huntsman quietly, thoughtfully led Utah to leading the nation in job creation. Jon Huntsman: Utah, No. 1. About the same time, another governor led Massachusetts. Led them close to the very bottom.”

Now, Huntsman’s shots at Obama are wrong — if “numbers never lie,” Huntsman knows the Recovery Act stopped the bleeding and created millions of jobs. But the point of the clip is Huntsman going after Romney, and pushing the former Massachusetts governor on one of Romney’s biggest vulnerabilities.

And why would Huntsman be going after Romney instead of Perry, since Perry is now leading in the polls? Remember, presidential primaries aren’t really as wide open as they might appear — candidates are targeting specific kinds of voters, groups, and constituencies. In this case, Huntsman believes the kind of voters he’s likely to impress are the kind of voters in Romney’s camp. If the former Utah governor can help bring down the former Massachusetts governor, his campaign will excel.

I’m skeptical this will work, but I am glad to see candidates start to notice Romney’s anti-jobs record. Remember, during Romney’s only service in public office, his state’s record on job creation was “one of the worst in the country.” Massachusetts really did rank 47th out of 50 states in jobs growth on Romney’s watch (and unlike President Obama, Romney didn’t inherit an economic crisis). There was a reason Romney served one term and then quit — he was not at all popular with his constituents and probably would have lost a re-election bid if he’d tried.

And that’s just his public-sector record. In the private sector, Romney made a living slashing American jobs — a record that’s also starting to gain wider attention and greater salience.

I know why Romney has decided to build his entire campaign around unemployment — it’s what voters care about most — but it would seem odd for Republicans to nominate the candidate whose weakest issue is jobs.

Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.