In Eastern Michigan since 2001, at least 21 Democratic public officials have been charged or linked to corruption inquiries, including the governor, the mayor of Detroit and several local officials, including Mr. Marlinga. Officials at the United States attorney’s office in Detroit identified one Republican who had been charged and said they did not have a list by party that would allow them to identify others.

Some of those Michigan cases resulted in convictions on significant charges. They included a member of the Pontiac City Council who pleaded guilty to taking a bribe from F.B.I. agents posing as local businessmen, a Detroit councilman convicted of fraud, and a former Wayne County official convicted of accepting gifts from a Detroit airport contractor.

On the other hand, several cases resulted in acquittals or no charges being filed, or convictions on relatively minor offenses. A Wayne County lawyer who pleaded guilty in 2004 to a misdemeanor charge, for example, used an intern to enter data on potential Democratic political donors for the pending governor’s race.

In Mr. Marlinga’s case, the State Republican Party and his Republican opponent in the House race filed complaints asking for an investigation. The charges centered on a legal motion by Mr. Marlinga, while serving his fifth elected term as county prosecutor, to the State Supreme Court in 2002 agreeing that it should re-examine a decade-old rape case. He had doubts about the case because an orthodontist who had appeared as an expert witness — testifying that there was at least a 3 million to 1 chance that a bite mark on the victim came from someone other than the suspect — had since been discredited. A second expert witness had recanted her testimony.

The testimony was crucial to the prosecution, and Mr. Marlinga said he felt morally obligated to notify the Supreme Court of his doubts. The convicted man was later acquitted, after the Supreme Court agreed that he should be retried.

But Mr. Marlinga’s request to review the case nearly ended his career as a lawyer. Several days before he filed it, he attended a holiday party where he solicited campaign contributions for his Congressional race, including a $2,000 donation from a real estate agent who employed the sister of the convicted man.

Mr. Marlinga knew that the real estate agent — who had no financial or family relationship with the rape suspect — believed that the man deserved a new trial. Mr. Marlinga said he saw no issue with accepting the donation, because he had decided months earlier to file the brief.