After telegraphing its intention for weeks, the Club for Growth on Monday formally endorsed former state Speaker Marco Rubio (R) in Florida’s Senate primary, setting up a marquee showdown with national GOP leaders, who are backing Gov. Charlie Crist.

The powerful anti-tax group is coming off high-profile involvement in the special election in New York’s 23rd district. In that contest, which highlighted an ideological rift between the conservative and moderate wings of the Republican Party, the club became a leading player in the successful effort to undermine the party’s nominee.

But while some conservatives are beating the battle drums for the ideological war to shift now to the Sunshine State, insiders don’t expect the club to play a starring role in Rubio’s effort to knock off Crist from the right.

That’s because there’s a difference between the group’s financial abilities in a Senate race compared to a House race.

“In House races, [the club] can in a sense be the single dominant financial player in a race,— said a source familiar with the club’s fundraising history and track record in previous cycles. “They have never been able to do that in Senate races and they are not able to now. … The club can play a supporting role … but [it] can’t carry the day on its own.—

Monday’s endorsement of Rubio came just days after the club announced the release of a new TV ad bashing Crist for his efforts to pass President Barack Obama’s economic stimulus plan earlier this year.

But while the club saturated television airwaves in upstate New York with ads leading up to the special election, it’s unlikely they’ll be able to do the same across a state as large and expensive as Florida.

Florida Republican consultant and former state Republican Party Executive Director David Johnson estimated Monday that it costs about $1.2 million to $1.5 million a week for 1,000 points of ads statewide in the primary. He noted that the cost would certainly be lower if a group were to focus its ad buys on cable or pick specific media markets to focus on, such as Orlando and Tampa where about half of the Republican primary electorate is based.

During the entire 2008 election cycle, the club’s PAC spent a total of $2.9 million on advertisements. The club’s 501(c)(4) arm spent another $2.7 million on advertisements.

Since he entered the race in May, Crist has raised more than $6.9 million.

The club may be more helpful to Rubio by moving contributions from a national donor base to the former state Speaker.

Last cycle, the club bundled $6.2 million in contributions from donors to its various candidates.

“Within Florida, Marco Rubio has tremendous difficulty competing with the governor for money,— Palm Beach County Republican Party Chairman Sid Dinerstein said. “For Marco to have enough money to make his case, he needs national fundraising, and Club for Growth is one of the key elements in that. It’s not that [the club will become] the fundraising arm of the Rubio campaign. … They are just one more element that allows Rubio to become competitive.—

Rubio is the fourth Senate endorsement the club has made this year, but it marks the first time this cycle where the powerful anti-tax group is directly opposing the preferred candidate of the National Republican Senatorial Committee and national party leaders.

The club and the NRSC are no strangers to being on opposite sides of a primary fight.

In 2006, Sen. Lincoln Chafee (R-R.I.) beat back a primary challenge from club-endorsed Cranston Mayor Steve Laffey only to lose the general election to now-Sen. Sheldon Whitehouse (D). In 2004, then-Republican Sen. Arlen Specter won a club-fueled primary challenge from then-Rep. Pat Toomey (R) and went on to win the general election despite conservative defections to a Constitution Party candidate.

Although it came up short in those marquee matchups against the NRSC, the club has found success in other open-seat Senate races.

In 2004, the club backed Sen. Tom Coburn (R-Okla.) in an open-seat contest despite the fact that by the time the former Congressman entered the race several national party leaders were already behind then-Oklahoma City Mayor Kirk Humphreys (R). That same year, the club also helped now-Sen. Jim DeMint (R-S.C.) fight his way through a crowded primary.

As it became more likely in recent weeks that the club would endorse Rubio, some Republican insiders have openly wondered if the group will go all in on the high-profile Florida primary and limit its participation in other races this cycle — such as Pennsylvania, where Toomey, a former club president, is back for another shot at Specter, who switched parties earlier this year.

But the source familiar with the club’s fundraising said that’s unlikely to happen.

“The reason it probably does not impact what they can or will choose to do in other races is that, from the bundling end of things, the club’s participation is really driven by the motivation of its members,— the source said. “There’s no finite pool [of money]. … They decide how motivated they are about the races.—

Over the years, some Republican critics of the club have complained that the group has occasionally given weak candidates the resources to get through tough primary races — only to abandon them when the general election comes around. Those critics point to Idaho’s 1st district race in 2006, where the support provided by the Club for Growth was a key reason Republican Bill Sali made it through a crowded primary, but the National Republican Congressional Committee had to step in during the general election to get Sali elected. Sali went on to lose his 2008 re-election.

“They can’t just take these people, get them across the [primary] finish line and walk away,— one Florida GOP aide said Monday.

In his release Monday, Club for Growth President Chris Chocola said the group’s political action committee had spent months studying the race and concluded that either Crist or Rubio would be heavily favored to win against likely Democratic nominee Rep. Kendrick Meek.

“The only question now is what kind of Republican will Florida send to Washington next year: a pro-growth Republican with a record of fiscal conservatism or a big-government Republican with a record of tax increases?— Chocola said.

An NRSC spokesman declined to comment Monday on the club’s endorsement.

Crist spokesman Eric Eikenberg said Crist “shares many of the same views as the Club for Growth, and he looks forward to working with them as Florida’s next Senator.—

Perhaps foreshadowing the Crist campaign strategy in the coming weeks, Eikenberg added that “there is a difference between candidate Rubio and Speaker Rubio.—