To no one’s surprise, the Club for Growth today endorsed Marco Rubio in the GOP primary for Florida’s open Senate seat. The move, which had been rumored for weeks, comes just a few days after the club ran an ad attacking Gov. Charlie Crist’s support of President Obama’s stimulus plan. “Marco Rubio is the real deal, one of the brightest stars in American politics today and a proven champion of economic liberty,” Club president Chris Chocola said in a release this morning. No question, it’s a huge endorsement for Rubio, who has been gaining the support of plenty of big-name Republicans in recent months, including Mike Huckabee, in spite of the fact that national party had already signaled its support for Crist in the nomination battle. Or rather, they had. Last week, Sen. John Cornyn, the Texan who runs the National Republican Senatorial Committee, told ABC his committee wouldn’t get involved in the state’s Senate primary—overlooking the fact that Cornyn had endorsed Crist months ago.

The big question is, What does this really mean for Rubio? Last week, the club disclosed it had spent $1 million on New York’s hotly contested special election for its 23rd congressional district seat. Its chosen candidate, Conservative Party candidate Doug Hoffman, narrowly lost the race, but the group’s spending sent chills through Republican ranks in Washington, who fear the group could use its war chest to challenge GOP candidates in other races. Yet, as your Gaggler reported last week, some Republicans pooh-poohed that idea, saying there was no way the club could afford to target too many races. One big reason: Pennsylvania. The group, which spent nearly $2 million on behalf of Pat Toomey’s primary challenge against Arlen Specter in 2004, is already expected to at least double that spending on the anticipated Toomey-Specter rematch next year. In Florida, the race is expected to be even more expensive, in part because there are more TV markets to hit. One estimate floated last week is that it would take at least $5 million for the club to have even a minimal impact on the race. Add to that other matchups the group is reportedly looking at, including primary races for open seats in Illinois and New Hampshire. Club officials say their fundraising is up, but is it enough to actively compete in what will no doubt be a very expensive election year?

Of course, it’s not just about the money the club itself will spend on Rubio’s race. It’s about the other doors their endorsement could open for him. Will it help Rubio become the cause du jour among other conservative activists and perhaps help him land other big-name endorsements—like, say, Sarah Palin? There are two immediate problems that Rubio faces in the campaign against Crist. One, he’s still largely unknown statewide. According to a recent Quinnipiac poll, 55 percent of Florida Republicans say they didn’t know enough about Rubio to have an opinion about him. The second problem: money. The former Florida statehouse speaker lags way behind Crist when it comes to cash in the bank. According the latest campaign-finance reports filed with the Federal Election Commission, Rudio had raised a little more than $1.6 million through Sept. 30, with roughly $930,000 in the bank—a pretty good sum for a guy challenging the establishment candidate. But it’s still not close to the more than $6.9 million Crist has raised this year. According to his FEC reports, the Florida governor still has just over $6.2 million in the bank.  With the primary not scheduled until next August, Rubio has time to catch up, but more immediately, he has to raise doubts, not just among GOP primary voters but among national GOP donors and activists, that Crist is vulnerable. The club’s ad attacking Crist was a big gift to the Rubio campaign, but, as Arian noted last week, Rubio is coming under increased scrutiny himself. He’ll need more than just the Club for Growth’s endorsement to remain competitive for the next nine months.