It’s worth taking a moment to appreciate how deadly serious conservatives are about ensuring that the McConnell escape-hatch proposal, should it come to that, does not pass the House — perhaps leading to default with untold consequences to follow.

The latest: Some eighty House Republicans have now signed a letter calling on GOP leaders not to even let the McConnell plan get to the floor for a vote, a GOP aide tells me.

As I noted here yesterday, one key metric for judging whether the McConnell plan can get through the House is a letter that Tea Party-backed Rep. Joe Walsh is distributing among colleagues. He’s hoping to amass 100 members on the letter, which would be a strong statement of opposition that would call into question whether the McConnell plan has any chance of passing.

The GOP aide tells me he’s roughly 20 signatures away from that goal. The letter with final signatories wil be released tonight.

So what does the 80 total mean? If the letter does get around 100 signatories, that would mean there are around 140 remaining Republicans. Even if all of them voted for the plan, that would mean you’d need roughly another 80 House Dems. That is probably gettable, though it may be difficult, given all the noise Dems are suddenly making against the proposal. One Dem aide tells me the question of how many Dems will support it turns heavily on the complexion of the $1.5 trillion in cuts that would be packaged with the McConnell proposal.

That all sounds pretty ominous. But it’s also possible, as Senate GOP and Dem aides are hoping, that there will be a drop dead moment of terror next week that will, shall we say, persuade people to rethink their positions a bit. The idea is that if “cut, cap and balance” fails in the Senate over the weekend, and folks realize early next week that a cuts-for-revenues deal isn’t going to happen, House Republicans will suddenly realize that they are about to take the blame for default and possibly economic catastrophe. Peering into the abyss will cause them to pull back rather than lean forward and plunge to their doom. So goes the hope, anyway.

Separately, the influential Club for Growth just blasted out an email on the Hill pressuring Republicans to sign the Walsh letter, threatening to take their position into account in evaluating each member’s record. Did I mention that these folks are dead serious about stopping this thing, the consequences be damned?