Johnson ran unopposed in 2008 as he sought re-election in his heavily Democratic district in suburban Atlanta. Now five candidates have lined up to run against him, including two high-profile Democrats.
In early February, Johnson completed an aggressive treatment of daily Interferon shots that left him irritable, alarmingly thin and occasionally depressed. Now he finds himself in what could be the toughest battle of his political life. Johnson realizes that his health issue might have opened the door for his opponents. But he also points to a wave of anti-incumbent sentiment that could present a challenge
Johnson, 55, said he's feeling strong -- his body free of the virus that was detected more than a decade ago -- and is ready for the heavyweight challenge he's expected for some time now.
He chalks up the new fight to a sense among some Georgia Democrats that he got lucky when as a little-known county commissioner in 2006 he ousted Cynthia McKinney, the firebrand congresswoman. Johnson entered the race a few months before McKinney struck a Capitol Hill police officer. Voters in McKinney's district -- used to her sometimes outrageous remarks -- had finally had enough and Johnson coasted to a runoff win.
"There's some disrespect," Johnson told The Associated Press on a recent swing through his district in DeKalb County.
"Folks are still wondering, 'How did he get elected?' " Johnson said. "They assume I benefited from the 'anyone but Cynthia' vote. But I have to claim full credit for realizing what the mood of the people was in the 4th District at that time."
The 4th Congressional District is heavily Democratic. In 2008, 79 percent of voters cast a ballot for Barack Obama compared with 20 percent for Republican John McCain. So, Johnson's toughest competition will almost certainly occur in the July primary when he'll face off against two seasoned opponents -- former DeKalb County Chief Executive Officer Vernon Jones and DeKalb County Commissioner Connie Stokes.
Stokes, 56, served in the state Senate for a decade before her 2004 election to the DeKalb County Commission where she's led the budget and finance committee.
The 49-year-old Jones made an unsuccessful bid in 2008 for the Democratic nomination to take on Saxby Chambliss for the U.S. Senate. Before taking the reins in DeKalb County he'd served in the state House of Representatives.
Both are plugging résumés packed with public service.
"Certainly I have more legislative experience than either of the other candidates including the incumbent," Stokes said, arguing the pivotal issue for her in the race is job creation.
Jones said he's balanced a budget, helped small businesses and helped create the state's PeachCare health insurance program for children.
"This is not a race I wanted to run," Jones said. "It was a call of necessity ... the people in this district need someone with my experience in Congress."
The Republican candidates are small business owner Liz Carter, management consultant Cory Ruth and Larry Gause, who supports elimination of the income tax.