Congressional Quarterly suggests that Cindy Sheehan's run against Pelosi will only help her nationally. The logic says that subjecting her to a challenge from the Left will make her appear more mainstream:
Yet some political analysts speculate that Sheehan’s candidacy actually could benefit Pelosi and her Democratic Party. While Sheehan is widely deemed as unlikely to pose a serious threat to defeat Pelosi, her arguments that Pelosi’s views are not liberal enough could provide a counterpoint to the contention often voiced by Republicans that the House Democratic leader is too liberal.
Pelosi has represented a liberal Bay Area constituency since winning a June 1987 special election and will seek an 11th full term next year. Republicans cast her as the embodiment of the “West Coast liberal” — and much as they did in the 2006 elections, GOP candidates are already invoking Pelosi’s name in their 2008 campaigns, warning their party base of what they contend is her determination to shift Congress far to the left.
But it is from the left that Sheehan is attacking Pelosi, which in turn might allow Democrats to cast the Speaker as more mainstream than she appears in Republican caricatures.
That's certainly a possibility, but I don't think there are many voters nationwide who pay that much attention. And of course, if Sheehan actually gets any traction -- something to be hoped for -- Ms. Pelosi will have to either forcefully argue that the pacifist apologist for Saddam and the Taliban is wrong, or she will have to echo Ms. Sheehan to appeal to her base. Either outcome would be welcome by Republicans.