A 35-year-old graduate of Harvard Law School is challenging ten-term Dallas Rep. Eddie Bernice Johnson (D) in a Tuesday primary that could be her most competitive in years.

To defeat Johnson, 76, political newcomer Taj Clayton will be fighting an uphill battle against all the advantages of incumbency. In February, Johnson received a rare Congressional-level endorsement from President Barack Obama, a crucial talking point in Texas' 30th District, which is 46 percent black.

Meanwhile Clayton, who served on Obama's 2008 finance committee in the state, is taking a page from the president's campaign handbook by portraying himself as an energetic agent of change. Whether he succeeds or instead faces the same fate that befell Obama in his failed 2000 primary challenge to Rep. Bobby Rush (Ill.) may depend in large part on how ready voters in the Texas district are to pass the political torch to a new generation of black leaders.

"President Obama is endorsing Eddie Bernice Johnson because she's a senior, black member of Congress," said Cal Jillson, professor of political science at Southern Methodist University and a longtime observer of Dallas politics who has met both candidates. "But Taj Clayton is the future."

The newcomer is mounting a credible challenge, judging by his fundraising numbers. Through May 9, he had raised $401,720. Johnson, by contrast, had raised $562,357, much of that through the political action committees that a long-serving incumbent like her can call on in a time of need.

Although enthusiasm for the president may have waned elsewhere in the country, it is still high in Texas' 30th District, judging by Clayton's near-rhapsodic memories of first hearing about Obama.

"Before he was the president, before he was a senator, we had some mentors in common who told me to put him on my radar," Clayton said. "The day he announced his candidacy in 2007, my wife and I immediately jumped on board."

Obama's candidacy may have been appealing to Clayton not just because he, too, was a young black professional who had grown up in the era after the civil rights movement scored its greatest successes.

Clayton, like Obama, grew up in modest circumstances. His parents, who moved the family to Dallas the summer between his senior year at high school and freshman year in college, worked at a glass factory. His grandparents were sharecroppers in Virginia in the 1930s.

"I worked my way through Harvard cleaning bathrooms and sweeping down steps," Clayton said. After completing his undergraduate degree, cum laude, he picked up a law degree after a brief stint in New York with his wife. Then he scored a clerkship with a federal judge before returning to Dallas to work as a commercial litigator at the high-powered firm Fish & Richardson.

Clayton said he would like to bring his experience to bear to help south Dallas.

"This area has suffered form a lot of problems that have persisted for a long time: low economic development, public schools that aren't doing well," he said. "There's been a lot of talk about improving our area and making it better, but not a lot has taken place."

It's the same sort of speech that powered Obama into political office. But Obama, in his run against former Black Panther Bobby Rush, was dogged by charges that as a University of Chicago lecturer who lived in Hyde Park, he was inauthentic.

Bernice Johnson and her allies are now making similar claims against Clayton, who lives in the middle-class Dallas suburb of DeSoto. A super PAC called Friends United, run by a former Johnson staffer, has spent $25,000 distributing a mailer that claims Clayton is "funded by right-wing extremists, supported by Republicans." Johnson's campaign swears she doesn't know anything about the super PAC -- but the group's rhetoric is strikingly similar to what the congresswoman has said in public appearances, lashing out in unusually harsh terms against a formerly unknown primary challenger.

Johnson did not return a request for comment.

Jillson, the professor, said the charge is "ridiculous … You just have to ask yourself, who would be convinced by that?"

But he believes that Johnson has some real advantages in the district. "She's right in (line with) the classic civil rights era politician, elected and oriented toward her overwhelmingly black and poor district," he said.

Johnson is not merely an incumbent, she is also a trailblazer -- the first black woman to represent North Texas in Congress. On her website she lists her membership in the Congressional Black Caucus, her support for consumer literacy and her steering of massive amounts of transportation funding to highway-mad Dallas as accomplishments.

Clayton has steered away from questioning the incumbent's successes. But Johnson's record has not been entirely absent of controversy -- in 2010, a scandal was revealed showing that Johnson had doled out Congressional Black Caucus Foundation scholarships to relatives -- but it seems not to have bothered constituents much.

"Eddie Bernice Johnson is popular in her district," Jillson said. "And so you can't go really hard against her without putting off voters in the district."

Clayton said his campaign has knocked on 30,000 doors and called 10,000 likely voters. His campaign's statistics on which of its likely supporters have taken advantage of early voting have him, he said, "pretty giddy, actually."

But for all of Clayton's seemingly boundless enthusiasm, Jillson is skeptical he will even be able to force Johnson into a runoff.

"I think Eddie Bernice is going to win, comfortably," Jillson said. Nevertheless, he predicted Clayton will do surprisingly well and best another primary challenger, Texas House Rep. Barbara Mallory Caraway, who did not return a request for comment.

"Taj Clayton will run second and in doing so he's run an impressive campaign," Jillson said. "He's young."