The floodgates have officially opened on the Republican leaders who are trying to hold together Member support, or at least minimize outright opposition, for the party’s nominee, Dede Scozzafava, in next week’s special House election in upstate New York.

On Tuesday, former National Republican Congressional Committee Chairman Tom Cole (Okla.), Sen. Jim DeMint (R-S.C.) and Rep. Dana Rohrabacher (R-Calif.) spurned the leadership by endorsing Doug Hoffman’s third-party campaign in the New York special election, following the lead of Rep. Todd Tiahrt (R-Kan.), who announced his support for Hoffman on Friday. Other national conservative GOP leaders, such as former Alaska Gov. Sarah Palin, Minnesota Gov. Tim Pawlenty and former Sen. Fred Thompson (Tenn.), have also endorsed Hoffman, and Thompson is now appearing in a Hoffman TV ad that began airing Tuesday.

But the defection of House Republicans is particularly noteworthy — especially Cole, who helmed the NRCC in the 2008 cycle and appears to be at odds with his successor at the committee, Rep. Pete Sessions (Texas).

One House Republican, who declined to be identified, said he was not surprised that his colleagues had backed Hoffman and predicted more members of the caucus would formally back the state Conservative Party nominee in the coming days.

Rep. Peter Roskam (R-Ill.) said the endorsements were “certainly not helpful.—

“I think if you could hit the reset button on the whole thing, you would,— Roskam said, expressing a sentiment no doubt shared by many in the GOP in what is turning out to be a divisive race for the party.

The public support for Hoffman among Members comes amid growing indications that he has a shot at winning the three-way race and that Scozzafava, a political moderate, is sinking.

In his letter endorsing the Conservative Party nominee, Cole called Hoffman “the only Republican who can win this special election.—

Democrats agree. “They’re running neck and neck,— Democratic Congressional Campaign Committee spokesman Ryan Rudominer said of Hoffman and attorney Bill Owens, the Democratic nominee.

As a result, the party is shifting its advertising attacks from Scozzafava to Hoffman, with a $245,000 ad buy this week criticizing Hoffman as out of touch and for supporting “failed— economic policies. The DCCC also raised the specter of Hoffman winning a seat in Congress to solicit funds Tuesday.

One Republican in the House said many members of the political action committee community now believe Scozzafava will come in third next Tuesday. “Is that dead in the water? I’d say that was pretty damaged,— the Republican said.

That sentiment conforms with a poll released Monday by a group allied with Hoffman, the anti-tax group Club for Growth, which had Hoffman in the lead. But the poll was based on a very small sample size. And the group released another poll earlier in the race that overstated Hoffman’s standing compared to an independent poll released soon after.

National Republicans say their polls do not show Scozzafava in third, and the National Republican Congressional Committee has pledged to stick by her. The NRCC reported $42,000 in ad spending going after Owens on Monday.

They further claim that the DCCC’s attacks on Hoffman are driven by the fact that he is drawing a big chunk of independents, which Owens needs. Hoffman led Owens and Scozzafava among independents according to a poll released last week by the liberal blog Daily Kos. It was conducted by the independent polling firm Research 2000.

“At the end of the day, endorsements from D.C. are not what’s going to decide this race,— NRCC spokesman Paul Lindsay said of the Members endorsing Hoffman on Tuesday. Both the NRCC and the Scozzafava campaign are emphasizing the longtime Assemblywoman’s local ties and experience representing the district’s issues, in contrast to Hoffman and Owens, who have never held office before.

Still, Cole’s nod in particular represents a slap in the face to the current NRCC brass.

A member of the Republican Steering Committee, Cole wrote that Hoffman “clearly represents the main stream values and positions of the Republican Party.— He declined to directly criticize Scozzafava, the subject of countless attacks from the right for her moderate record in the state Assembly, but he ticked off a number of issue areas where she and Hoffman diverge. “He opposes the stimulus, cap-and-trade, card check, the Democratic health care bill and the Obama administration’s reckless spending binge. He is a pro-life fiscal conservative who is committed to restraining the growth of government,— Cole wrote.

Rohrabacher called Hoffman “the only candidate in the race that shares my conservative Republican principles,— and DeMint wrote in a piece on the conservative blog RedState.com that “Doug Hoffman has stepped forward and offered voters a better choice— in the race to succeed former Rep. John McHugh (R). McHugh resigned the 23rd district seat in September to become Army secretary.

The endorsements came on the same day that the Hoffman campaign launched a new TV ad featuring Thompson, who deems the candidate a “principled conservative.— The Club for Growth, whose endorsement of Hoffman in September provided the campaign its initial surge of momentum, also announced it would begin airing a new TV ad Tuesday in the Watertown, Burlington, Vt., and Syracuse media markets highlighting the differences between Hoffman and Owens. Scozzafava is not mentioned in the new spot.

“This special election is now between Hoffman and Owens, and their economic records couldn’t be more different,— Club for Growth President Chris Chocola said in a statement.

Democratic surrogates are also ignoring Scozzafava to go after Hoffman. On Tuesday, the American Federation of State, County and Municipal Employees reported a $200,000 ad buy via its PAC to attack Hoffman. The progressive group Accountable America, founded by leading liberal campaigner Tom Matzzie, a former official of MoveOn.org, is spending $25,000 on an ad buy critical of Hoffman’s ties to the Club for Growth and Wall Street, part of what it said in a statement is “a larger six-figure campaign on the financial crisis in NY-23 and elsewhere.—

And veteran Democratic strategist Paul Begala sent an e-mail to DCCC supporters Tuesday on the race that read, “The inmates have taken over the asylum, and are abandoning the Republican candidate in favor of the extreme conservative.—

“This could either be a cause for concern or a great opportunity,— he continued, urging readers to contribute to the DCCC and help get a “Democrat elected in a district that hasn’t sent a Democrat to Congress since 1852.—

Jackie Kucinich contributed to this report.