In order to increase pressure on House Republicans to pass the Senate compromise on the two-month payroll tax cut extension, Dems are pointing out that John Boehner seemed to previously indicate that the House GOP would support it — before getting an earful from his caucus and nixing his backing of the plan.

The idea Dems are pushing is that Boehner has lost control of the volatile Tea Party wing of his caucus and is unable to muster unity among House Republicans behind a proposal that passed the Senate by 89 votes. Dems are casting the House vote on the Senate compromise as a key test of his leadership, arguing that a No vote will show Boehner las lost control — a storyline Republicans reject.

Democrats are still hoping that by increasing the pressure on Republicans, the Senate extension could pass the House today. House Dem leaders have now sent a letter to Dem members urging them to vote for the measure in “overwhelming” numbers, a Dem aide tells me. If the vast majority of Dems support it, only around two dozen Republicans would have to vote Yes in order for it to pass. Nancy Pelosi has denounced the House GOP’s latest maneuver as a “made up crisis.”

Speaking to reporters today, Boehner insisted that the Senate compromise would not pass the House and that he had never supported it. “I raised concerns about the two-month process from the moment that I heard about it,” Boehner said.

How does that square with the timeline of events? Last Thursday, Boehner said: “If the Senate acts, I’m committed to bringing the House back — we can do it within 24 hours — to deal with whatever the Senate does.”

Asked to square those two statements, Boehner spokesman Michael Steel told me that Boehner had merely pledged to vote on the Senate’s compromise, not to support it. “We are acting on what the Senate produced — we’re voting on it tonight,” Steel told me. “He said ‘act,’ not ‘support.’”

But CNN quoted a source over the weekend saying that Boehner had called the Senate compromise a “good deal” on a conference call. Meanwhile, Roll Call reports that Boehner was in touch with Mitch McConnell while the Senate deal was negotiated, suggesting the possibility that he may have been supportive before his caucus rebelled.

Boehner spokesman Steel conceded that there had been contact, but disputed the importance of it. “We always keep in close contact with Senator McConnell’s office — but that doesn’t mean our respective Conferences will agree on every issue,” he said.

Republicans are arguing that Boehner never said House Republicans would support the Senate compromise — and that he never expressed support for it — in order to push back on the notion that he’s lost control of the caucus amid the volatility of the Tea Party wing. But if the House votes down the Senate compromise tonight, Dems will only amplify that case.

UPDATE: On Monday night, the House GOP leadership decided not to proceed with the vote, and will instead try to negotiate changes to the Senate bill in conference negotiations. Dems claim that Republican leaders decided against a vote because they were afraid the Senate bill would pass.