Yesterday, the Club For Growth launched a new attack ad against Gov. Charlie Crist (R-FL), a moderate who is facing a challenge in the GOP primary for Senate from the more conservative former state House Speaker Marco Rubio -- which was, in fact, a change from the Club's previous skepticism about getting involved in this race.

Back in July, when Crist was much further ahead in both polls and fundraising, the Club's executive director David Keating had said the Club was still looking at where it could best spend its money: "We have to look at his race versus all the others we're interested in, and there are going to be a lot of competitive races."

Today, Keating told TPM that Rubio's recent pick-up in fundraising, taking in about $1 million for the previous quarter, was an encouraging sign.

"Well I think the ad stands on its own. It's not meant to be an endorsement or something that says he [Crist] shouldn't be governor or Senator. But I would say we're definitely leaning into that direction of endorsing Rubio, but we haven't made any final decision yet," said Keating. "The thing that got us more interested was the more recent fundraising report by Rubio. And I think I've consistently told media in response to inquiries, it's our belief that Rubio doesn't need to match Crist dollar for dollar to win, but he does need enough money to get his message out in Florida. So we're guessing he probably needs $4 million or $5 million for this race."

Keating also said that the recent decision to go after Crist was not influenced by the Club's success in promoting Doug Hoffman in the NY-23 special election, in which he overtook moderate GOP nominee Dede Scozzafava and narrowly lost to Democrat Bill Owens. Keating said Rubio faces the challenge of attracting attention as one of many races -- and of getting it soon enough to make a difference.

Keating was even surprised by the degree of national attention that Hoffman got, with figures like Gov. Tim Pawlenty (R-MN) endorsing him over the regular Republican. "Will this happen for Rubio? I don't know, it might," said Keating. "If it happens, when will it happen? Will it be early enough for him to do something with it?"