If there is one candidate who truly wishes that Christine O'Donnell had not won the Republican senatorial nomination in Delaware, it is the Republican Senate candidate in Pennsylvania, Pat Toomey. A former congressman, Toomey became a hero to the Right for pushing Sen. Arlen Specter out of the GOP. For much of the summer, Toomey ran safely ahead of the man who went on to knock out Specter in the Democratic Senate primary, Rep. Joe Sestak.

Then came O'Donnell's defeat of Rep. Mike Castle in one of the tea party's most celebrated victories. Northern Delaware happens to be part of the Philadelphia media market and the attention lavished on O'Donnell, her sometimes exotic views and her "I'm not a witch" TV spot spilled over state lines.

Sestak, who won his primary in the face of President Barack Obama's support for Specter, has taken full advantage, arguing that Toomey may be stylistically different from the colorful candidate across the river, but is substantively quite similar. Toomey was president of the conservative Club for Growth, a group that targeted moderate Republicans in primaries, and Sestak says his opponent and O'Donnell both want to drive middle-of-the-roaders out of the GOP.

You might also imagine, from all the times he cites it, that Sestak's favorite book is Toomey's 2009 supply-side manifesto, The Road to Prosperity, which endorses private accounts for Social Security and a moratorium on all corporate taxes.

"Congressman Toomey is not a witch," Sestak loves to say, "but his book is very scary."

All this has allowed Sestak to close the gap with Toomey and move momentum to his side. Toomey's campaign argues that Sestak has simply brought some Democrats home and can point to some recent polling favorable to the Republican. But Toomey tacitly acknowledges the damage O'Donnell has done him because he now carefully delineates his differences with her.

And the O'Donnell effect has larger implications. Republican gains next week are inevitable. But if Senate candidates on the right end of Republican politics lose here and in most of the other states they are contesting (Colorado, Wisconsin, Alaska, Kentucky, and Nevada), conservatives will have trouble claiming this election as an ideological mandate and a sign that the country had moved well to the right of where it was two years ago.

So far, being righter-than-right has been anything but helpful. O'Donnell's nomination virtually sealed a victory for Democrat Chris Coons. In Colorado, Democratic Sen. Michael Bennet, after spending the summer under assault from anonymously funded conservative groups, has been closing in on tea-party favorite Ken Buck. In Wisconsin, Sen. Russ Feingold has narrowed Republican Ron Johnson's once substantial lead.

In Alaska, the tea party's Joe Miller faces a formidable write-in challenge from Sen. Lisa Murkowski, whom he defeated in the Republican primary, even as Democrat Scott McAdams battles to sneak through on the GOP split.

Republican Rand Paul has clung to a lead over Democrat Jack Conway in Kentucky, a very red state where a Republican should not be having so much trouble. As for Nevada, nobody knows if Senate Majority Leader Harry Reid will prevail over marquee tea party candidate Sharron Angle, but Angle's bizarre brand of conservatism is the one thing giving Reid a fighting chance.

A Sestak victory would be an especially powerful tonic for progressives because the former admiral has been brave in supporting trials for the Guantanamo detainees and a ban on assault weapons.

He has also been unabashed—and far more entertaining than most Democrats—in defending his votes for the stimulus, health-care reform and the Wall Street rescue. In one ad, he likens voting for the financial bailout to cleaning up after his adorable puppy Belle. The analogy is between the puppy's mess and the one created by the economic policies of Toomey and former President George W. Bush.

What comes across when you talk with Sestak is an utter lack of defensiveness. Democrats, he says, "should be proud of what they've done." But he's impatient that leaders of his party (he doesn't mention names) have failed to convince voters that Washington fully understands their struggles and their aspirations. Naturally, he makes the point with a Navy idiom. "You don't run a ship from the bridge," he says. "You run it from the boiler room." Leaders, he says, need to persuade voters "that we know who they are."

A Sestak victory would certainly be a major defeat for tea-party-style conservatism. But it would also offer progressives lessons in how to develop a down-to-earth outside game of their own. 

(c) 2010, Washington Post Writers Group

Related: Bitter Brew, by the Editors; Extreme Makeover, by E. J. Dionne Jr.