This shouldn’t be held against him, but it probably will be.

The caucus members are Rand, Sen. Mike Lee, R-Utah and South Carolina Sen. Jim DeMint, who backed Rubio’s fledgling Senate campaign even as the Republican party backed former Gov. Charlie Crist. They will meet in a Senate office building with leading tea party activists including Campaign for Liberty president John Tate, Americans for Tax Reform president Grover Norquist and Tea Party Express chairman Amy Kremer…

Kremer, who said the tea party movement is aimed at “sending conservatives to Washington, not Republicans,” acknowledged a “little bit of disappointment” that it appears Rubio “won’t be standing with Sen. DeMint, Lee and Paul.

“Ultimately what matters is his vote, but there is concern,” Kremer said. “All these new members should know that we are watching. If anybody thinks they can play this movement, that’s not going to happen. We’re watching what they say, what they do.”…

“It would be nice if he joined Rand Paul’s caucus, but as long as Marco continues to vote in the way we’d like to see him vote, that’s the most important thing,” said Steve Vernon, vice president of Tea Party Manatee on Florida’s west coast. “As long as his vote and his actions and his word continue to essentially mirror our principals, then we’re not really upset.”

Click the image below to watch Rubio explain his thinking to the Shark Tank. He’s been publicly skeptical of a Senate Tea Party Caucus since at least last July, and I myself have made some of the same points that he makes here: Is there any purpose to a TP Caucus beyond providing grassroots tea partiers with a symbolic beachhead on the Hill? And isn’t it odd, and maybe counterproductive, for a deliberately leaderless, anti-Beltway movement like the tea party to have congressmen suddenly coopting its brand? That said, if there’s interest among grassroots conservatives in a Senate caucus along these lines, why wouldn’t a popular young pol want to pander to them by joining?

The obvious answer: Unlike DeMint, Paul, and Lee, Rubio has national ambitions. And as an exceptionally savvy retail politician, he knows that he’s more likely to achieve those ambitions by voting the tea party way without wearing the tea party label. It was slightly more than a year ago that the NYT dubbed him the “first senator from the tea party,” and ever since then he’s been quietly inching away from it — a prescient move given all the negative attention to people like Angle and O’Donnell in November. No less a tea party authority than Dick Armey of FreedomWorks started nudging candidates like Rand Paul last summer to identify as Republicans rather than TPers because the tea-party label will draw extra attacks from the left without adding any extra benefits from the right. Case in point: Tom Coburn. Not a guy who waves the Gadsden Flag regularly, but a guy who’s nonetheless deeply respected on the right for his record. That’s what I think Rubio’s aiming for more or less — a Coburn-esque stature among conservatives for his record and an Obama-esque appeal to centrists via his youth, charisma, and relative soft-spoken-ness.