Congressman Rick Renzi, an Arizona Republican, was locked in a close re-election battle last fall when the local United States attorney, Paul Charlton, was investigating him for corruption. The investigation appears to have been slowed before Election Day, Mr. Renzi retained his seat, and Mr. Charlton ended up out of a job — one of eight prosecutors purged by the White House and the Justice Department.

The Arizona case adds a disturbing new chapter to that scandal. Congress needs to determine whether Mr. Charlton was fired for any reason other than threatening the Republican Party’s hold on a Congressional seat.

Mr. Renzi was fighting for his political life when the local press reported that he was facing indictment for a suspect land deal. According to The Wall Street Journal, federal investigators met unexpected resistance from the Justice Department in getting approval to proceed and, perhaps as a result, the investigation was pushed past the election.

Mr. Renzi’s top aide, Brian Murray, admitted this week that when reports surfaced that his boss was being investigated, he had called Mr. Charlton’s office asking for information. Mr. Charlton’s office did the right thing, according to Mr. Murray’s account: it refused to comment. Weeks later, Mr. Charlton was fired.