Nancy Pelosi has had a very bad stretch over the issue of what she knew, and when, about waterboarding and other “enhanced interrogation techniques.” She still seems not to have learned that it’s a bad idea to get in a public spat with people who collect secrets for a living. Her ever-shifting explanations of what she was briefed on and when, culminating in yesterday’s press conference (in which a visibly shaken Speaker repeatedly re-read her prepared statement in answer to questions by a suddenly skeptical press corps) have left her credibility in tatters and her story wholly incoherent. The latest blow came today as Leon Panetta, her former House colleague and now Obama’s CIA director, produced a memo today disputing Pelosi’s contention that the CIA lied to her: “CIA officers briefed truthfully on the interrogation of Abu Zubaydah, describing ‘the enhanced techniques that had been employed.’”

Just as bad for the Left, her flagrant hypocrisy on this issue has badly undermined their core argument for prosecuting members of the Bush Administration. Recall that the theory behind such prosecutions is that waterboarding is so obviously “torture” that no reasonable person could conclude otherwise – yet here is the leader of their lawmakers in the House declaring that she very reasonably assumed that if Bush Administration lawyers had cleared the practice, it must be legal. (Charles Krauthammer makes this point as to the moral argument). That’s an impossible circle to square, and it means the cries of “war criminal” now have to be seriously muted and nuanced if the most left-wing Speaker in memory is not to be sacrificed to a left-wing crusade.

It’s too soon to tell what sort of lasting damage will be done to Pelosi as Speaker. I’m not generally one to declare a politician dead the minute a bad story breaks. More likely, as happened to Newt Gingrich and Tom DeLay, it will take multiple blows to bring down Pelosi, and the impetus will have to come from the rank and file of her own caucus, which seems disinclined to toss her under the bus just yet (even if the heir apparent, her longtime rival Steny Hoyer, has been fairly unsubtly measuring the drapes in the meantime).

That said, there’s a school of thought among Republicans that because Pelosi is a polarizing figure with obvious weaknesses, we should fear pushing too hard because the Democrats will be weaker for having her around their necks next fall than if she’s gone (one hears similar sentiments about Chris Dodd, David Paterson, and Deval Patrick, among others). Let her twist in the wind, these voices say. But even aside from the legitimate interest in exposing dishonesty and hypocrisy on the part of a sitting Congressional leader, the hard calculus of political hardball says otherwise. Of course, in any debate there are arguments that work and those that don’t, and in this particular debate there are punches that may need to be pulled for legitimate national security reasons. But Republicans serious about winning political battles going forward should not ease the pressure on Speaker Pelosi out of some misguided hope that leaving her wounded is better than finishing her off.

There are two reasons for this. The first is the brutal calculus of political hardball: when you have the enemy down, you finish her off, lest she recover and be stronger, and your ammunition stale, by the time you fire again. You don’t let her get up and catch her breath and try to get her own counter-narrative out. You can’t predict the flow of events, and you can’t predict with certainty how much damage any particular charge or revelation might do, so better to use what you have when you have it, and get the most you can. This is how the Democrats took on Gingrich and DeLay and, for that matter, Bush – and the accumulation of damage eventually took its toll. There are rare exceptions to this rule: for example, Rahm Emanuel knew for months in 2006 that he had 100% damning stuff on Mark Foley, but since it was so damaging and Foley was a comparatively small fish by himself, it made sense for Rahm to keep quiet and have the story go off closer to the election. But that’s the exception, not the rule.

Second, even if – as seems more likely – this story doesn’t really have enough juice to take out Pelosi all by itself, it’s undeniably become a serious distraction. And that itself is a thing of great value right now. Quick: in the past three decades, how many times has a political party passed a major domestic policy priority through legislation more than six months after taking control of the White House or one or more Houses of Congress? I don’t know the answer either, but I’m pretty sure it’s “not many.” This is a point I have noted in regard to the Bush Administration, and it’s just as true of the Democrats: they will not have an unlimited window of opportunity in which to nationalize health care and pass a ruinous cap-and-trade program, major tax hikes, EFCA, and other significant priorities. The clock is already ticking four months into the Obama Administration, with the summer recess gradually creeping closer and a potential major battle brewing over the Supreme Court. Every day that the Speaker is tied up defending herself over an issue the Democrats thought would help them is a day that her attention, and the headlines, are pulled away from the rest of the legislative agenda. Even Republicans who would like to keep Pelosi around another year for electoral advantage have to realize the even greater priority on stopping that agenda now, for the good of the country.

The Pelosi story has mostly taken on a life of its own by now, and/or is being driven by sources in the CIA or elsewhere in the intelligence community; much of this is in any event beyond Republican control. But if Republicans get the opportunity to keep the heat on the Speaker, they should.