"Never before has there been such a compelling case for impeachment and removal from office of the president of the United States," Anderson was expected to tell Washington lawmakers during his testimony.
The mayor outlined his case against the commander in chief, including "misleading" Congress and the public about the need to go to war in Iraq, violating international treaties by invading and occupying Iraq, authorizing unconstitutional warrantless wiretapping of U.S. citizens and allowing the torture of prisoners.
Anderson also submitted written testimony - a 22-page, footnoted brief that said it wouldn't be an overstatement to label Bush a "war criminal."
And at a rally earlier in the day on the Capitol grounds, the mayor referred to his hometown.
"As mayor of the capital city of the reddest state in the nation, I am proud to join with millions of good, patriotic Americans who are standing up and willing to raise their voices against this madness," he told scores of protesters.
Anderson, a Democrat, was slated to be one of two pro-impeachment speakers at Washington's Government Operations and Elections Senate Committee in support of a resolution urging Congress to investigate whether Bush and Vice President Dick Cheney should be impeached.
The resolution is sponsored by Democratic Washington state Sen. Eric Oemig. The group Washington for Impeachment paid for Anderson's trip.
The resolution, however, is seen as a long shot. Top Democrats in Washington state, including the governor and two members of Congress, have urged state lawmakers to curb impeachment discussions, according to The Associated Press.
It is seen as a distraction and unwise.
According to the AP, a spokeswoman said Democratic U.S. Sen.
Patty Murray told Washington Democrats: "I have two words for anyone who wants to impeach the president: Dick Cheney."
Even with other states considering similar resolutions, the White House isn't worried. When asked about possible investigations and impeachment with a majority Democratic Congress in early January, White House press secretary Tony Snow said: "The president is going to be doing his job."
Tribune reporter Thomas Burr contributed to this story.