Criticism from the Rev. Markel Hutchins and state Rep. "Able" Mable Thomas came even as the challengers praised Mr. Lewis for his long record of public service.
Mr. Lewis, the Rev. Hutchins and Ms. Thomas are seeking to be the Democratic candidate for the majority black 5th Congressional District of Georgia, which spans Atlanta and Fulton County, and includes parts of Clayton and DeKalb counties. Mr. Lewis has served as the district's representative since 1987 and has not faced a Democratic challenger in 16 years. The primary is July 15.
Mr. Lewis' early endorsement of his friend and colleague, former Democratic presidential candidate Sen. Hillary Clinton, caused controversy and drew condemnation from some in the black community. Weeks after the Georgia primary election, Mr. Lewis defected from Mrs. Clinton's campaign as it became clear that black voters were overwhelmingly for Barack Obama.
Repeated calls to Mr. Lewis' campaign headquarters on Wednesday seeking comment about his decision to skip the debate were not immediately returned.
Ms. Thomas called into question Mr. Lewis' judgment on the war in Iraq, which the congressman initially voted to support, and said that Mr. Lewis has not been focused on his constituents.
"You've spent so much time being a national leader and forgotten the pain and suffering of the 5th district," Ms. Thomas said, addressing her question toward the vacant spot reserved for Mr. Lewis. "They have no way to get in touch with you, no way to get through to you."