First Assistant U.S. Attorney Robert Cessar has been named acting U.S. Attorney for the Western District of Pennsylvania, The Pittsburgh Tribune-Review reports. Mary Beth Buchanan, who was named the office’s head prosecutor in 2001, resigned on Monday.

While Buchanan did not announce her official plans, she has been in discussions with local Republican party leaders about running for the Republican nomination to challenge  Rep. Jason Altmire (D), who represents Pennsylvania’s 4th congressional district.

Cessar has served in the office since 1990 and had held the position of first assistant since 2002. He was previously an attorney for the Federal Deposit Insurance Corporation in Washington. Cessar can hold the acting title for 210 days. President Obama has yet to nominate a replacement. Democratic Sens. Arlen Specter and Bob Casey haven’t announced whether they’ve made recommendations to Obama for any of Pennsylvania’s three districts.

Western District of Pennsylvania U.S. Attorney Mary Beth Buchanan will step down tomorrow, leaving office with one regret, the Pittsburgh CBS affiliate KDKA reported.

Mary Beth Buchanan (DOJ)

The controversial Bush holdover, who has served as U.S. Attorney since 2001 and also held a Justice Department position in Washington during the Bush years, told the television station that she wishes she never approved a plea deal with comedian Tommy Chong in a drug paraphernalia case called Operation Pipe Dream.

Chong, who starred in the “Cheech & Chong” movies, agreed to plead guilty to one count of conspiracy to distribute drug paraphernalia through a family business to save his wife and son from prosecution. He was sentenced in 2003 to nine months in prison and was ordered to pay a fine. It isn’t clear from the KDKA article why Buchanan regretted the plea deal, but Chong’s prosecution had sparked protests by civil libertarians and ridicule for Buchanan’s office.

Buchanan told KDKA she had no regrets about another case that her critics questioned, the unsuccessful prosecution of former Allegheny County medical examiner Cyril Wecht.

Her office dismissed all charges against the Democratic defendant after a federal judge threw out evidence that he ruled was improperly obtained. Wecht’s supporters accused Buchanan of targeting him because of his politics. Former Attorney General Richard Thornburgh asked Attorney General Eric Holder to discipline Buchanan for “vindictively” suggesting at a news conference that Wecht was guilty, but nothing ever came of the request – at least publicly.

Buchanan didn’t tell KDKA about her future plans, but said she is considering another public office. We reported that she might run for the Republican nomination to challenge  Rep. Jason Altmire (D), who represents Pennsylvania’s 4th congressional district.

Western District First Assistant U.S. Attorney Robert Cessar is slated to serve as acting U.S. Attorney until a successor to Buchanan is confirmed by the Senate, according to the television station. Pennsylvania Democratic Sens. Arlen Specter and Bob Casey have yet to announce their recommendation for the post.