Serves them right, if Democratic leaders in Harrisburg are worried now that independent presidential candidate Ralph Nader has landed on the November ballot.

It was due to the Democrats' successful challenge of Nader's petition signatures in 2004 that the long-time consumer watchdog and political gadfly was tossed off the ballot when John Kerry ran against President Bush.

That alone would be enough to fire up Nader supporters to do the job right this time. That they have done. The campaign this month filed more than twice the number of signatures required to get on the ballot, with Nader officials pledging they were far more careful to avoid bogus signatures.

Wonder what got the Nader forces so fired up? Well, they had a special incentive for payback:

In the recent indictment of 12 Democrats on charges of doing campaign work on state salaries, Attorney General Tom Corbett alleged that Democratic operatives worked, in part, on the Nader ballot challenges. The operatives did the same number on 2006 Green Party U.S. Senate candidate Carl Romanelli, Corbett said.

If those allegations prove true, there's a good measure of justice in Nader's successful petition drive. Bad enough that Pennsylvania erects some of the most onerous barriers to candidates getting on the ballot. It's even worse if entrenched political interests play dirty.

That's not to excuse the fact that the 2004 Nader campaign did a shoddy job with its petitions. But the presiding judge who said the Nader petition drive "shocks the conscience of the court" may want to revise his view in light of how Nader was targeted by Democrats. Indeed, the Corbett revelation makes the case for Nader's plea to overturn the order that he pay more than $81,000 in legal costs run up by the Democrats.

This isn't an endorsement of Nader's candidacy. But there shouldn't be any underhanded tactics in challenging his or anyone else's earned appearance on the fall ballot. Nader's candidacy remains a quixotic mission that is bound to be of more use to John McCain than Barack Obama, but he has earned his spot.