This is the second in an occasional series analyzing Georgia’s five competitive congressional primary races ahead of the May 20 vote, as the state’s delegation to Washington is set to go through a historic shift. Coming in the weeks ahead:

  • 10th District: Six Republicans compete for the nomination to succeed Rep. Paul Broun of Athens, who's running for the Senate seat being vacated by Sen. Saxby Chambliss.
  • 11th District: Former congressman Bob Barr is widely viewed as the man to beat in the crowded race for the 11th congressional district's Republican nomination to replace Rep. Phil Gingrey, who is running for the Senate seat being vacated by Sen. Saxby Chambliss. Five other Republicans are competing with Barr.
  • 12th District: Five Republicans are vying to compete with Augusta Rep. John Barrow, the last white Democrat from the Deep South in the U.S. House and an elusive target for Georgia Republicans over the years.

U.S. Rep. Hank Johnson may be in his toughest fight yet to hold onto his Atlanta-area congressional seat.

The four-term congressman’s opponent in the May 20 Democratic primary — former DeKalb County Sheriff Tom Brown — enjoys strong name recognition in the 4th Congressional District and is running a well-funded campaign.

The stakes are high. No Republican has qualified to get on the ballot. So the Democratic primary’s outcome will decide the general election winner.

“It is going to be highly contested,” said Steve Anthony, a former executive director of the Georgia Democratic Party who now teaches political science at Georgia State University. “At this point and time I would say it is a tossup.”

The heavily Democratic district covers much of DeKalb and Newton counties, stretches across a big chunk of Gwinnett County and swallows all of Rockdale County. All those counties except for Gwinnett picked President Barack Obama in the 2012 election.

Last month, the president endorsed Johnson, a former DeKalb commissioner who served as co-chairman of Obama’s 2008 presidential campaign in Georgia.

But in a troubling sign for the soft-spoken congressman, Johnson had less campaign money on hand than his opponent at the end of December, an unusual circumstance for a longtime incumbent.

At the end of December, Johnson had just $85,297 left on hand compared with Brown’s $108,019. Brown formally entered the race in late October, but he began raising money months earlier through an exploratory committee. He also gave his campaign a $20,000 loan.

Both Johnson and Brown support the federal health care overhaul and Obama’s efforts to revamp the nation’s immigration system. With few policy differences between them, they are picking at the sources of each other’s campaign funds. Johnson pointed out that some of Brown’s donors have aligned with Republicans. Among them: Brad Alexander, a political consultant who previously served as chief of staff to Republican Lt. Gov. Casey Cagle; and Jay Davis, the chief executive of the National Distributing Co. and a GOP donor.

“I am the real Democrat in the race,” Johnson said in a recent interview at the This is It! BBQ and Seafood restaurant in Lithonia. “The only way that people can determine what kind of policies my opponent would likely support if he were to win the seat is by looking at his campaign contribution list.”

Brown shot back that Johnson received campaign contributions from Republicans when he defeated then-U.S. Rep. Cynthia McKinney in a fierce Democratic primary runoff that drew national attention in 2006. Among the Republicans who gave to Johnson’s campaign then: Guy Millner, who ran unsuccessfully for governor in 1998, and former state Rep. Emory Morsberger of Gwinnett.

Brown also criticized Johnson for getting most of his campaign money from political action committees instead of individuals. PACs have contributed 92 percent of Johnson’s campaign funds compared with 3 percent for Brown, according to opensecrets.org, the website of the Center for Responsive Politics, a nonpartisan research group that tracks money in politics.

“The fact that I have been able to raise what I have raised from individual contributions — primarily — is a testament about how people feel about my leadership,” Brown said in an interview after delivering a speech last week at the resortlike Park Springs retirement community in Stone Mountain.

A tall man with a deep, booming voice, Brown frequently emphasizes his ability to work across political aisles. He served as DeKalb’s fire chief before winning election four times to be the county’s sheriff. He resigned from that job this year to run for Congress.

Complaining that unemployment rates are too high and that the middle class is not growing, Brown accused Congress — and Johnson — of inaction.

“(Johnson) has not initiated any meaningful legislation since 2007,” Brown said. “It appears that he is waiting for someone else to pass some legislation that he would vote up or down, depending on what the president wants.”

A spokesman for Johnson vigorously disputed that assertion, emailing The Atlanta Journal-Constitution a list of 62 bills the congressman has introduced since 2007. Among them is 2013 legislation aimed at helping the U.S. secure access to precious minerals used in clean energy and defense manufacturing. A 2007 bill he sponsored supports providing federal grants to local law enforcement agencies.

Johnson rejects the notion that he is embroiled in his most difficult fight yet to hold onto his seat. He said he faced his toughest challenge in the 2010 Democratic primary, when he defeated former DeKalb CEO Vernon Jones and then-DeKalb Commissioner Connie Stokes.

“I don’t view this one with the same degree of uncertainty as I did with that race,” Johnson said.

Johnson added he was struggling with Hepatitis C — a blood-borne liver disease — when he was facing off against Jones and Stokes. The congressman said he is now cured after taking medication.

“It’s amazing how good health feels,” Johnson said. “I tell you I feel real good and I’m at the top of my game physically.”

Johnson has repeatedly drawn attention in Congress for his unscripted comments, like the time he jokingly asked in 2010 whether posting more U.S. troops in Guam might cause the island to tip over. Or the time last year he sarcastically praised House colleagues for approving legislation to save the nation’s helium reserve, rather than dealing with federal budget cuts caused by sequestration.

“Imagine, Mr. Speaker, a world without balloons,” Johnson said before mentioning the “injustice” of not having helium for comedians to alter their voices.

A staunch Obama supporter, Johnson is trumpeting the president’s endorsement. Brown predicts that won’t have much of an impact in the race.

“This is not about who loves the president the most,” Brown said. “This is about being a strong voice and (bringing) strong leadership inside the halls of Congress.”

Gary Noble was among those who listened to Brown’s speech at the retirement community in Stone Mountain. The retired public health worker said he likes Brown’s views on overhauling the nation’s immigration laws and is leaning toward voting for the former sheriff.

“He’s a very articulate, fresh voice,” said Noble, a former rear admiral with the U.S. Public Health Service.

Count Charles Primus among those planning to vote for Johnson. The retired plumber sat near Johnson at This is It!, polishing off a meal of oxtail, cabbage and banana pudding. Primus said he agrees with Johnson’s emphasis on domestic affairs and his dovish approach in conflicts with other nations.

“Take care of home,” Primus said, “and everything falls in line.”

Both candidates are predicting victory next month.

“I feel very good about my chances,” Brown said. “I believe I am going to be the next congressman.”

And Johnson: “Voters know me. They know my record. Given that there is no compelling reason that my opponent gives for making a change, I think that I should win re-election.”