After months of preaching a more laid-back approach to leadership and allowing the House to “work its will,” Republican leaders Tuesday reluctantly opened the traditional legislating playbook and started leaning on their rank and file to line up behind Speaker John Boehner’s debt limit proposal.

But they face a daunting task, as House conservatives, outside groups and Senate brethren all are coming out against the Ohio Republican’s plan.

Majority Leader Eric Cantor (Va.) led the charge for leadership, demanding that his Members “stop grumbling and whining” about Boehner’s plan and rally around the Speaker before it is too late.

Majority Whip Kevin McCarthy’s (Calif.) team also swung into action, pressing reluctant Republicans to back the measure, which it described as “the last Republican train out of the station,” warning that a failure to pass the bill could turn a Senate Democratic proposal into a must-pass measure.

And while leaders publicly and privately attempted to keep up the appearance of confidence, they acknowledged it was far from certain that Boehner’s bill would pass.

“It may be too late” to play hardball with the GOP Conference, a veteran Republican aide warned.

In fact, despite the pressure, Members rolled out their opposition just hours after Boehner went on national television Monday night to argue for his plan.

Republican Study Committee Chairman Jim Jordan (Ohio) on Tuesday said, “I am confident, as of this morning, that there were not 218 Republicans in support” of Boehner’s proposal. His comments took leadership off guard and angered top Republicans, who were frustrated by his decision to discuss GOP whip counts publicly.

“It may be the last train leaving the station … [but] I’m sure leaning against it,” Rep. Jeff Flake (R-Ariz.) said Tuesday.

Other Republicans who have joined the chorus opposing the Speaker’s bill include Reps. Louie Gohmert (Texas), Michele Bachmann (Minn.), Connie Mack IV (Fla.), Chuck Fleischmann (Tenn.), Steve Southerland (Fla.) and Tim Huelskamp (Kan.).

Others, such as Rep. Scott Garrett (N.J.), are leaning toward opposing Boehner’s bill or, at best, remain undecided.

There have been some bright spots for Boehner. Rep. Allen West, who signed a letter demanding that a balanced budget amendment be sent to the states before he would vote for a debt increase, said Tuesday that he will support Boehner’s bill. “This Boehner plan doesn’t have everything that I wanted … [but] that’s part of what you have to have here in Washington, D.C.,” the Florida Republican said.

Likewise, the U.S. Chamber of Commerce came out in support of the bill, saying it would make a “yes” vote on the measure a key vote, which might help shore up moderates and business-minded freshmen. On Monday, Americans for Tax Reform gave the plan its blessing as well.

Still, even those who said they were leaning toward voting for the bill appeared to do so reluctantly.

“Is it a great proposal? No. [But] we’re one House against a Democratic Senate and Democratic White House,” said Rep. Sean Duffy (R-Wis.), one of several fence-sitters who said they were leaning toward supporting it.

Part of the problem for Boehner is that he and his leadership team have never taken a strong-arm approach, and many conservatives did not appear to be moved by their sudden reliance on traditional hardball tactics. “Yes, they may not respond well” to those efforts, Duffy said.

Boehner also finds himself squaring off against his home-state colleague Jordan, whose chairmanship of the RSC gives him a potent power base.

Boehner must also contend with intense pressure from outside organizations, many of which helped elect last year’s massive freshman class and which have long-standing ties to his Conference’s conservative wing.

Heritage Action for America, which opposes Boehner’s plan, announced Tuesday that the bill would be a key vote. Similarly, the Club for Growth on Tuesday announced it “strongly opposes the Boehner debt limit plan” and would also make the measure a key vote.

Former Rep. Ernest Istook (R-Okla.), a distinguished fellow at the Heritage Foundation, was actively engaged in pushing back against Boehner’s plan. According to House aides, Istook was on the floor Tuesday night urging Members to vote “no.”

There are rules regarding former Members’ access to the floor, particularly those that work for think tanks, lobbying shops, nonprofit organizations and trade associations. At press time it was not immediately clear whether Istook’s activity was a violation of House rules. A Heritage spokesman did not return a request for comment.

The Cut, Cap and Balance Coalition — a grass-roots group of tea party and conservative activist organizations that spearheaded the Cut, Cap and Balance proposal Republicans have backed — reiterated its opposition to Boehner’s bill Tuesday.

“While we salute Speaker Boehner for his indefatigable efforts to forge some new agreement breaking the debt ceiling stalemate, we cannot support his latest package. It is both bad policy and a violation of the Cut, Cap and Balance Pledge,” the group wrote in a memo to lawmakers.

And across the Capitol, there lurked more trouble. Sen. Jim DeMint (R-S.C.), the conservative kingmaker, came out against Boehner’s proposal, using his network of activists and donors to disseminate Heritage Foundation critiques of the legislation Tuesday. Other Republicans, such as Sens. Mike Lee (Utah) and Rand Paul (Ky.), also came out against Boehner’s plan.

The influence that DeMint and activist organizations carry among freshmen and the party’s conservatives cannot be underestimated. Particularly when matched against Boehner, who has always been viewed with suspicion by ideological purists, these groups, at a minimum, are making life difficult for Boehner, Cantor and McCarthy as they round up votes.

When asked if he was backing the measure, Rep. Lee Terry (R-Neb.) quipped, “Good question. Once I figure it out I’ll tell you.”