WASHINGTON -- Republican prospects in next year's Senate races are not good, with most analysts forecasting deeper GOP losses, though they could be offset by some Democratic upsets.

Democratic Sen. Chris Dodd of Connecticut is running behind in the polls as a result of the role the Banking Committee chairman played in the housing-bubble debacle and the sweetheart mortgage deal he got from a pal in the mortgage industry he oversees.

And in Pennsylvania, Democratic convert Arlen Specter's recent party switch may be backfiring on him, as Democratic voters reconsider the longtime Republican's voting record and cool to his candidacy, according to recent polls showing only 28 percent say he deserves re-election. The prospects of a party primary challenge further endangers Specter's bid for survival and gives Republican hopeful Pat Toomey a chance for an upset.

But trouble may be brewing for Republicans in Florida where the Club for Growth, a conservative anti-tax group, is seriously considering running ads in the GOP's primary race against Gov. Charlie Crist for supporting higher state taxes and President Obama's $800 billion economic-stimulus spending plan.

Crist's opponent for the GOP's Senate nomination next year is former state Speaker of the House Marco Rubio, the son of Cuban immigrants and a young, up-and-coming party leader running on cutting government spending and taxes where Crist may be especially vulnerable.

Rubio secretly met here recently with the Club for Growth, which has a reputation for defeating liberal-to-moderate Republicans in party primaries with its aggressive ad campaigns.

"We recently interviewed Marco Rubio and were impressed. We are very concerned about the two major tax increases Charlie Crist recently signed and believe there's no excuse for his active support of the Obama big-government stimulus spending bill," said David Keating, the Club's executive director. "We are actively considering the race."

Rubio is largely unknown among the state's voters, and head-to-head polls show the popular governor with a large early lead over the former state representative. But Rubio told me in a recent interview that in a state that has no income tax, Crist is beatable on fiscal and tax issues once his record is more widely known.

Polls show that voters have grown more doubtful about Obama's big-spending stimulus and are especially worried by the massive government debts that they fear will short-circuit any economic recovery. And that's the dynamic that Rubio now thinks will turn next year's primary contest into a close race.

"There are stark differences between the candidates on fiscal issues," said Alex Burgos, spokesman for the Rubio campaign. "The governor signed a budget on May 27 that included $800 million in fee increases and a $1-per-pack cigarette-tax increase."

Rubio, on the other hand, is calling for the elimination of all property taxes on primary residences and replacing it with a controversial flat consumption or sales tax, modeled in part on the FAIR tax proposal at the federal level. Tax-cut crusader Grover Norquist, who heads Americans for Tax Reform (ATR), has praised Rubio, calling him "the most pro-taxpayer legislative leader in the country."

Norquist's grassroots organization expressed deep disappointment that Crist "went against his commitment to Floridians and broke his pledge as governor to oppose and veto any and all tax increases."

"The news was particularly surprising," since Crist recently "signed the federal Taxpayer Protection Pledge in his race for the U.S. Senate," ATR said in a statement.

Right now, Crist remains the odds-on favorite to keep the open Senate seat in the GOP's column. But if the Club for Growth, flush with cash, gets into the race, that could help Rubio with both money and message. Club membership "has never been higher," and the grassroots group has earned notoriety for winning upsets in party primaries, though not always with good results in the end.

For example, the Club last year opposed incumbent Republican Rep. Wayne T. Gilchrest on Maryland's Eastern Shore in his primary. He lost to conservative Andy Harris, who was defeated by Democrat Frank Kratovil in the general election.

Moreover, most of the Club's victories have been in congressional districts where it's cheaper and easier to have an impact in lower-turnout primary races. But party strategists question just how effective the Club could be in one of the costliest media markets in the country and whether they would be able to spend the kind of big money needed to change the direction of the race.

All of this has made life more complicated for Sen. John Cornyn of Texas, the National Republican Senatorial Committee's chairman who recruited Crist.

To be sure, the governor is a proven vote-getter who is seen as the only candidate capable of winning in a state that has become a lot more competitive in recent elections.

But taxes and spending have become the GOP's strategic issues in its bid to repair a damaged brand, and the party's restive base is in no mood to vote for anyone seen as going soft on either one of them.