House Minority Leader Nancy Pelosi (D-Calif.) warned her Caucus Tuesday that “there will be no passes” for any Democrat who bolts the party and votes with the GOP on Medicare legislation.

Pelosi, described as “fighting mad” by one Democratic leadership aide, told participants at her weekly leader’s luncheon that she will not tolerate any defections on the vote, tentatively slated for the end of the week and on which both Democrats and Republicans are whipping furiously. Democrats view prescription drugs as one of their signature issues and are pushing for close to unified opposition to the measure.

“Either you are on the team or you’re not,” said one House Democratic aide of Pelosi’s Caucus call.

“She said, ‘This is a party vote,’” added another well-placed Democratic aide, saying that while no specific consequences were laid out, the leader made clear she “will remember” how Members vote on the bill.

Key Democratic aides and lawmakers estimated that between 15 and 20 Members were seen as potential votes for the GOP-crafted bill. Pelosi and Minority Whip Steny Hoyer (Md.) met throughout the day with Members, seeking to push the numbers even lower. Nine House Democrats backed the bill when it first moved through the chamber in June, and the bill ultimately passed by one vote.

Even as the leaders turned up the heat on their Caucus, infuriated Democratic lawmakers were resigning their memberships from the AARP in response to the seniors’ group announcement Monday that it would back the prescription drug measure.

House Democrats were furious that the group — a longtime political ally — joined the GOP on a measure they believe will serve as nothing more than an election year prop for the majority.

Rep. Alcee Hastings (D-Fla.), who led the effort to encourage Democrats to bail on the organization, spoke at Pelosi’s lunch, telling his colleagues: “I resigned from AARP. We must all resign.” California Reps. Lois Capps and Lynn Woolsey both resigned as well, with Woolsey issuing a “Dear Colleague” letter later in the day calling on other Democrats to follow suit.

On the Republican side, leaders convened a blizzard of meetings in their effort to come up with the best possible count of lawmakers who planned to support the bill.

They were still awaiting the results of the first comprehensive whip count last night, but leadership aides expressed confidence that they would be able to draw enough support from their side of the aisle that they would not need to depend on Democratic defections.

Majority Whip Roy Blunt (R-Mo.) met with his Assistant and Deputy Whips on Tuesday morning and later huddled with the lobbyists who are heading up the GOP’s coalition effort.

As the Whip team fanned out to query each lawmaker on Medicare, all of those Members who said they were opposed or leaning towards opposing the bill were asked to provide their specific objections to the measure. Members will be grouped by complaint, and then Blunt and Cantor will meet with the smaller groups to try address their concerns.

At the GOP Whip meeting, Ways and Means Chairman Bill Thomas (R-Calif.) and Energy and Commerce Chairman Billy Tauzin (R-La.) took turns explaining the bill and trying to bat down counterarguments. They also sought to hammer home the point that the addition of some sort of prescription drug benefit to Medicare was inevitable, and that if Republicans don’t do it now, Democrats may do it in the future in a way that did not also include reforms aimed at holding down costs.

Republican leaders also hope the inclusion of medical savings accounts will be enough to lure some wavering conservatives, who were uneasy about the bill when it first passed the House.

But conservative Rep. Jeff Flake (R-Ariz.) predicted that many of his fellow conservatives would still be inclined not to support the bill.

“Health savings accounts — that’s good. It’s wonderful,” Flake said. “But is it enough to swallow everything else? I don’t think so.”

And while the AARP endorsement may provide political cover for moderates, Flake suggested it could actually have the opposite effect on some conservatives.

“Have we sold out that much?” Flake said of the AARP backing. “The National Taxpayers Union is scoring it the other way.”

Of all today’s meetings, the Republican Study Committee’s gathering could prove to be most pivotal. The conservative group’s members are currently split on the Medicare measure, and even RSC Chairwoman Sue Myrick (N.C.) said Tuesday that she had not had enough time so study the bill and thus was not sure yet whether she would vote for it.

Many Democratic Members, meanwhile, were echoing Pelosi’s call for unanimity, including Rep. Marion Berry (D-Ark.), who told the Caucus at the Pelosi lunch to stick together: “We must not give them a single vote — do not help them with this vote. I do not belong here if this is what it takes. If you go with this, you do not belong in this party.”

Hoyer, meanwhile, was working with Democrats — both individually and in groups — to lay to rest any confusion about the 1000-plus page bill. He held more than a dozen whip meetings Tuesday, trying to solidify opposition among Members by selling it as flawed policy that will not improve senior’s drug coverage.

The Whip, who also spoke at the leader’s lunch, said: “This is not about party, but about policy.”

Democratic leaders believe they cannot hope to do much better in keeping Members in line than they did in June, according to one well-placed aide, who added that there are “a lot of people who are undecided.”

“If we can keep it to nine, we win,” the staffer said of the vote.

One of the yes votes in June, Rep. Earl Pomeroy (N.D.), said there is pressure from Democratic leaders to reverse his earlier course, saying: “They have made it clear they want a ‘No’ vote.”

But Pomeroy said pressure aside, he will vote based on what is best for his district. He remains undecided, but is analyzing the bill with Democratic North Dakota Sens. Kent Conrad and Byron Dorgan.

Leadership believes Democrats can effectively sell their opposition to the Medicare measure, even though seniors have been pushing for a prescription drug bill for some time. Specifically, House Democrats insist the bill will ultimately lead to the privatization of Medicare, ultimately increase health care costs and cut benefits.

“It will be a very simple message,” said Rep. Ron Kind (D-Wis.). “People get that, they understand that.”

Once they push that message to seniors, regardless of the AARP endorsement, Democrats believe they can survive a potential political hit, and even score a victory.

“We are going to fight these birds,” said Rep. Bill Pascrell (D-N.J.) said of the Republicans. “If they think they have an edge on us, they are wrong.”