Mr. Lewis, 68, is on the ballot for Tuesday's 5th District primary with a 31-year-old minister and a state legislator who unsuccessfully ran against Mr. Lewis in 1992 and is 18 years his junior.
The Rev. Markel Hutchins and Rep. "Able" Mable Thomas are betting that Mr. Lewis' early endorsement of Mrs. Clinton will hurt him among voters who may have seen the alliance as a betrayal in a district that overwhelmingly favored Mr. Obama.
Mr. Lewis later switched his support to Mr. Obama and does not expect it to hinder his campaign.
"I told my young opponents, I've been about change. I am change," Mr. Lewis told The Associated Press. "If it was not for the changes that I, along with many of my colleagues, created, they probably would not have an opportunity to be running for Congress or anything else."
The winner of the 5th District primary will claim the seat and head to Washington in January, as there is no Republican candidate running for the post.
The Rev. Hutchins, who is among the youngest congressional candidates in the country, said his candidacy is meant not as an offense, but as a sign of gratitude.
"We thank Congressman Lewis and the generation that he marched with that brought us across bridges in the 1960s, but there are additional bridges to cross," the Rev. Hutchins said.
He gained national attention as spokesman for the family of Kathryn Johnston, the 92-year-old woman gunned down by Atlanta police officers in a botched 2006 drug raid. In the aftermath, he advocated for changes in police department policy and helped keep attention on the case.
Ms. Thomas, 50, also forged her political roots at a young age. She was chosen as a presidential delegate to the 1984 Democratic National Convention and won her first term in the state legislature at 28 as Georgia's youngest state representative. Her first stretch in the state legislature ended in 1993, after she first challenged Mr. Lewis for the 5th District seat.