A letter being circulated by freshman Rep. Joe Walsh (R., Ill.) could effectively take the contingency plan being crafted by Senate leaders Harry Reid (D., Nev.) and Mitch McConnell (R., Ky.) — it’s being referred to as “McConnell-Reid” — completely off the table in debt-ceiling negotiations.

Walsh tells National Review Online that he has received close to 90 signatures on his letter, which is addressed to House Speaker John Boehner (R., Ohio) and Majority Leader Eric Cantor (R., Va.) and urges them to publicly denounce the McConnell plan (or some version thereof) and ensure that it never comes up for a vote. He says that “people close to leadership” have told him that they are aware of the letter and the number of signatures (nearly 40 percent of the Republican caucus) and that it has “had an impact” on their decision making. In all likelihood, Boehner cannot afford another mass defection within the caucus (as with the continuing resolution to avoid a government shutdown in April).

McConnell’s plan has faced virulent opposition in the House from day one, primarily from the freshman and conservative members responsible for the “Cut, Cap and Balance” legislation that passed on Tuesday. Even some Democrats don’t like the plan. But GOP leadership has refused to rule it out. “If we’re unable to get to an agreement, it might look pretty good a couple of weeks from now,” Boehner said at a press conference last week. “I think it’s worth keeping on the table.”

“It’s always been a very, very, very last resort,” a House leadership aide tells NRO. “But no one likes it.”

If the impact of Walsh’s letter is to effectively preclude (or render moot) a vote on the McConnell plan in one form or another, it would be a significant development in the ongoing stalemate over the debt ceiling, because (despite the recent resurrection of the Gang of Six) many believe that McConnell-Reid is the most realistic — and perhaps only — way forward at this point.

Walsh says his office has been contacted by Senate staff members — Republican and Democratic — who have been asking about the letter’s popularity. Greg Sargent reports that some Senate GOP aides were hoping it would receive no more than 50 signatures. That hope went out the window quickly, however, once the conservative groups Club for Growth and Heritage Action joined the effort and, in a rare twist, announced they would “key vote” whether or not members signed on to the letter.

Walsh suggests that the success of his effort could have prompted the Gang of Six to unveil their proposal when they did as “a last-ditch effort to delay,” once it became clear that McConnell-Reid could not possibly pass the House. Beyond that, he says of the Gang’s plan, “I don’t think there’s anything there.”

“The rank and file, through the letter, is making that clear that [McConnell-Reid] is not going anywhere in the House,” he says. “I think the grand plan was, if I had to guess, everybody in leadership wanted to fall back on the McConnell plan. So pretty quickly the Gang of Six reappeared.”

Walsh is still collecting signatures, and plans to deliver the letter to leaders sometime tomorrow. By then he hopes to have at least 100. Stay tuned.

UPDATE: Sen. Saxby Chambliss (R., Ga.), a member of the Gang of Six, tells reporters that the House “probably has” killed the McConnell-Reid option and Senate leaders are working on alternatives ways to proceed.