Ralph Nader never lets go of anything.

He wouldn't let go of his campaign for auto safety in the 1960s, during which he became the bane of Detroit and almost single-handedly brought seat belts to American cars.

He wouldn't let go of his long-shot run for president in 2004, though Democrats said it might have cost John Kerry his chance to beat George W. Bush.

And he won't let go of what he believes was a wrong done to him by the Pennsylvania courts in 2004, when they knocked him off the ballot in the Keystone State, accused him of "extensive fraud" in the gathering of his nominating petition, and ordered him to reimburse $81,102 in legal fees rung up by the foes who sought to get him out of the race.

On Monday, Nader publicly released a letter he sent last week to Chief Justice Ronald D. Castille in which he suggested that Pennsylvania courts have undermined democracy by making it very difficult for third-party candidates to gain ballot access.

Nader told Castille it is "never too late" to change a bad decision, and warned him that voters "no doubt will take a keen interest" in the case if Castille decides to stand for retention election in 2013.

Nader, at 77 still active in environmental and antiwar issues, clearly remains stung by the personal rebuke given him by James Gardner Colins, president judge of Commonwealth Court, in 2004.

Colins said Nader's ballot petition was "rife with forgeries" and was "the most deceitful and fraudulent exercise" he had ever come across in court.

As a third-party candidate, Nader needed 25,697 valid voter signatures to get on the fall ballot, while the major candidates - Kerry and Bush - needed 2,000 to enter their party primaries that spring.

He said he submitted 51,273 signatures, "but the court ruled that only 18,818 of them were valid."

In his letter to Castille, Nader continued to insist there was "no evidence" of fraud - unintentional lapses, yes, but no fraud. Many of his signatures were invalidated on technicalities such as a voter's not using his full name, he said.

He complained that Castille ignored evidence, which came out later in a Bonusgate trial, that state employees on state time illegally helped a Pittsburgh-based law firm, Reed Smith L.L.P., compile evidence of his erroneous signatures.

The firm was working on behalf of Democratic state leaders. According to testimony, Nader said, Reed Smith attorney Efrem Grail ran the joint operation. Castille, he noted in the letter, previously worked at Reed Smith.

Castille declined comment to The Inquirer on Monday. "The chief is aware of the letter," said Tom Darr, the deputy state court administrator.

Grail did not reply to a request for comment left for him with a Reed Smith spokeswoman. But the firm issued a statement taking note of a judicial finding that Nader's campaign knew in 2004 that "some of [its] signature-gatherers had engaged in fraud, forgery, and deceit for personal gain."

Nader, in a telephone interview from his Washington office, said he would not give up on his fight to avoid having to pay the full $81,102 to Reed Smith. Part of that amount has been seized from an account he held with a Pennsylvania bank. He is battling efforts to take the rest from a Washington account.

He said Reed Smith already has had to absorb "tens of thousands of dollars" in costs while pursuing him for the money.

"This is going to be the most expensive move in terms of cost-benefit that Reed Smith has ever conducted," he said.

Samuel C. Stretton, a Pennsylvania lawyer who represented Nader for a time in his 2004 court fight, said Monday that Nader's stubbornness can be both a strength and a weakness.

"He is a very difficult man to work with," Stretton said. "He had his own opinions and has a great ego. . . . On the other hand, these qualities do him well when there are serious issues that have to be addressed. He has the courage and the toughness to do so."

Nader, who ran for president in 2000, 2004 and 2008, said he hadn't made up his mind about next year. But a run is "not likely," he said.

Contact staff writer Tom Infield at 610-313-8205 or tinfield@phillynews.com.