In politics, not all endorsements are created equal.

Many are perfunctory, simple reminders of overlapping agendas between the politician on the ballot and the person or group providing the plug. Endorsements in this category rarely resonate because they are entirely expected. Put business group endorsements for Republicans and labor for Democrats in this column.

Some come off as obligatory. Examples here include endorsements based on shared membership in a political party.

Some are clearly the result of negotiated deals, even if the terms don’t surface until after Election Day.

And some are just ridiculous, including the occasional all-is-forgiven runoff nod from a losing primary contender who’d just spent months depicting his or her chosen candidate as a truly terrible choice.

Then there are the rare endorsements that actually cause people to sit up and take notice. Put Republican Lt. Gov. Jay Dardenne’s decision to back Democratic state Rep. John Bel Edwards over Republican U.S. Sen. David Vitter for governor in this category.

If Dardenne had picked Vitter, following a bitter primary fight in which the senator ran grossly misleading ads about the lieutenant governor’s past legislative votes and ethics, the announcement would have fallen somewhere between obligatory and ridiculous.

Dardenne wouldn’t have been the first politician to pick party over personality. But if he’d tried to make the case that Vitter would be a good governor so soon after having called him “ineffective,” “vicious,” and “lying,” and having described his prostitution scandal as a “stain” on Louisiana, well, nobody would have listened.

They might well listen to his arguments for backing Edwards, though, even if they think his decision is at least somewhat personal.

Some of its power comes from the fact that it’s both counterintuitive and risky. The easy choice is always to stick with party, and indeed, the state GOP quickly cast the former LSU student body president as Louisiana’s Nick Saban. Ouch.

Even more powerful is the story it tells. Dardenne finished fourth in the primary, but he retains an image as an honest official and straight shooter, and his endorsement bolsters Edwards’ claim to be the more virtuous choice.

“Honor, integrity, truthfulness, openness and ethical behavior are the most important traits in public services. John Bel is the candidate who exemplifies these traits,” Dardenne said at the pair’s joint news conference Thursday morning.

Dardenne’s also a political moderate with good relationships across party lines, and his nod sends the message that Edwards would seek to bring people together.

More importantly, it directly undermines Vitter’s main argument, that electing Edwards would be akin to making President Barack Obama governor.

That’s far-fetched anyway, given Edwards’ conservative stands on some issues and the Legislature’s Republican majority. Still, Dardenne not only put his credibility behind the counter-argument; he also offers his own presence in Edwards’ circle as collateral. Under other circumstances, rampant rumors that Dardenne might join an Edwards administration could smack of a deal, but in this case, it’s more likely to be reassuring. Besides, a job as, say, commissioner of administration would hardly be cushy in this era of rampant budget woes; some might even call it a punishment rather than a reward.

Contrast Dardenne’s Edwards endorsement with former Gov. Mike Foster’s nod for Vitter, which was announced a day earlier. Foster is a fellow Republican, but the two were never really close allies. In fact, one of Foster’s main go-to guys in the Legislature during his two terms was Dardenne, then a state senator.

Foster’s statement on the race focused mainly on ideology. Vitter has “clear, strong, conservative Louisiana principles,” he said, while “the Democratic Party gaining control of Louisiana scares me.” That’s exactly what you’d expect a major Republican figure to say, and that alone limits its reach.

Dardenne, meanwhile, is positioning himself as something of an unlikely, albeit complementary, running mate. And in doing so, he’s making some real noise.

Stephanie Grace can be contacted at Follow her on Twitter @stephgracenola.