(CNN) -- Montana's chief federal judge has offered his apologies for forwarding a racist e-mail aimed at President Barack Obama. The judge also initiated a judicial misconduct investigation against himself.
Liberal advocacy groups demanded that U.S. District Judge Richard Cebull resign.
Cebull, in an interview Wednesday with the Billings Gazette newspaper, offered his regrets for forwarding the e-mail, saying it was "a hard lesson to learn."
"To say it's inappropriate and stupid is an extreme understatement," Cebull said in courthouse chambers on Wednesday, according to the newspaper. "There is no doubt it's racist. It wasn't forwarded for that purpose. If anything, it was political."
The Billings-based judge was named to the bench by President George W. Bush in 2001. He has been chief judge since 2008, overseeing two other full-time district judges, three senior or part-time judges and five magistrates. His chambers did not return a call from CNN for comment.
Cebull did not write the offensive material, but admitted forwarding the February 20 message to a few friends after it was sent to him by his brother. The Great Falls Tribune newspaper was given a copy and reported the message went:
"Normally I don't send or forward a lot of these, but even by my standards, it was a bit touching. I want all of my friends to feel what I felt when I read this. Hope it touches your heart like it did mine.
"A little boy said to his mother, 'Mommy, how come I'm black and you're white?' His mother replied, 'Don't even go there Barack! From what I can remember about that party, you're lucky you don't bark!'"
Obama is of mixed race.
Cebull said in the interview his conduct in court over many years has shown he is not a racist, but he admitted the public got that impression from the e-mail. "And I don't blame them," he added.
The judge also separately told the Great Falls Tribune, "The only reason I can explain it to you is I am not a fan of our president, but this goes beyond not being a fan. I didn't send it as racist, although that's what it is. I sent it out because it's anti-Obama."
Cebull has initiated a process under which a judicial misconduct complaint will be filed and an investigation will start, court officials said.
"Cebull has publicly acknowledged that he has acted inappropriately," Appellate Court executive Cathy Catterson said in a statement. "Judge Cebull has initiated the process by which a complaint of judicial misconduct will be brought against him. The Judicial Council is expected to act expeditiously in investigating and resolving this matter."
Some legal organizations said the apology was not enough.
"If he has any respect for his office and for ideals of equality and human dignity on which our country was founded, Judge Cebull will step down today," said Bob Edgar, president and CEO of the left-leaning nonprofit Common Cause. "The message he has acknowledged circulating demonstrates a lack of judicial temperament that ought to disqualify him from further service."
It's rare and generally very difficult to force federal judges from office. They receive tenure, and the Constitution guarantees they can remain on the bench "during good behavior."
Standards warranting removal are not clear, beyond a violation of civil or criminal law. Congress would have to initiate impeachment proceedings, but the few judges to face that have usually resigned before those proceedings went far.
There is no indication the judge in Montana would be subjected to that.
Before being nominated by Bush, Cebull worked as a federal magistrate judge in Montana from 1998 to 2001.