Clinton needs to do something dramatic. Take the bull by the horns, show that she's not just an overly scripted politician who will never do anything that's isn't "safe."
An excellent way to do that would be to leave the campaign trail and go back to Washington with Chris Dodd to filibuster retroactive immunity for the telecoms. The message that "nobody should be above the law," that she'll fight for accountability and won't be held hostage by big money interests would be a powerful one. She'd certainly grab all the media attention by doing so, and force Obama to either follow her lead or stay behind on the campaign trail while she goes to Washington and fights for the constitution -- neither of which have good optics.
It would be decidedly un-Penn like, unsafe and virtually impossible to poll. But it might be just the kind of shaking up that her campaign -- and the race as a whole -- would benefit from.
It's a really interesting idea, and would certainly build credibility for Clinton on the leadership front. Obama's (and Edwards's) weakness, heretofore unexploited, is that, though he's running on a message of change, he's never actually led on any substantive change. So Obama is something of a cipher. Clinton needs to emphasize this uncertainty and contrast her readiness to lead by doing something bold and dramatic. The FISA fight is Bush's top priority this year, and bringing some partisan heat to a national security issue might help reposition her as the candidate able and willing to make real change instead of just inspiring people with vague rhetoric.