Ralph Nader continues to shine an unflattering light on Pennsylvania's political system, with good reason.

Nader wrote a letter this week to state Attorney General Tom Corbett (a candidate for governor), calling attention to court testimony about Democrats' effort to knock Nader off the presidential ballot in 2004.

A witness in the ongoing corruption trial of former high-ranking Democratic Rep. Mike Veon testified recently that employees of the legislature worked on state time and used taxpayer-funded resources to challenge Nader's candidacy in court. Democrats believed Nader would take away votes from presidential candidate John Kerry in the contest against President George W. Bush.

Democrats succeeded in disqualifying Nader. A court found that his nominating petition was "rife with forgeries."

Democrats also are accused of using taxpayer funds to torpedo the third-party Senate candidacy of Carl Romanelli in 2006 to help the campaign of Democrat Bob Casey.

Allegations that elected officials used state resources illegally for political purposes are at the heart of Corbett's long-running prosecution in the scandal known as "Bonusgate." The Republican prosecutor has brought charges against 25 defendants in both parties, including former Speaker John M. Perzel (R., Phila.) and powerful Democratic Rep. Bill DeWeese (D., Greene).

Nader has raised valid questions about Corbett's judgment, too. In 2008, Corbett accepted $15,900 in donations to his reelection campaign from lawyers at a high-profile Pittsburgh law firm, Reed Smith, which had worked closely with Democrats on their court case against Nader.

Corbett's campaign accepted this money within weeks of the attorney general's charging House Democratic officials with corruption, including their campaign against Nader. No action was taken against the law firm, however, opening up Corbett to accusations that he went easy on campaign contributors.

Corbett had decided, correctly, not to accept contributions from legislators, who might be touched by his wide-ranging probe. He should have done the same with Reed Smith. A search of online state records showed no donations yet from Reed Smith employees to Corbett's gubernatorial campaign.

The attorney general showed similar poor judgment in allowing a top Perzel aide to hold a fund-raiser for Corbett during the Bonusgate investigation in 2007.

A source at Reed Smith said the firm cooperated with the attorney general's probe. The source said the firm worked on the Nader petition on a volunteer basis, and lawyers were not aware that some Democratic staffers from the legislature allegedly were working on state time.

None of this absolves the Nader campaign for obtaining fraudulent signatures in 2004. Nader did get on the ballot in 2008 in Pennsylvania fair and square.

But the picture we're left with isn't pretty — a state in which Democrats employed dirty tricks funded by taxpayers against a third-party candidate, and the state's top prosecutor with larger ambitions turned a blind eye to some potential conflicts.