Mayoral candidates David A. Catania, Carol Schwartz and Muriel E. Bowser took to the stage at American University on Thursday night for their first televised debate. Front-runner and Democratic nominee Bowser and independent candidate Catania set the tone for the debate, engaging in a number of sharp exchanges over education, ethics and political experience. (Ashleigh Joplin/The Washington Post)

Nearly six months of political tension let loose on the stage of an American University auditorium Thursday, with mayoral candidates Muriel E. Bowser and David A. Catania sparring testily over ethics, education and more during the general election’s first debate.

The debate, billed as a “conversation with the candidates” by the university and several co-hosts, turned quickly into a nastier affair. Early exchanges between Bowser, the Democratic nominee, and Catania, an independent, set an aggressive tone for the 90-minute debate and highlighted the high stakes of the evening, which also featured independent candidate Carol Schwartz.

“If we’re going to interrupt each other, it’s going to be a long debate,” Catania said early on, amid an exchange about ethics reforms. Yet plenty of cross talk ensued.

The first of four scheduled debates came on the heels of an NBC4/Washington Post/Marist poll that shows Catania and Schwartz struggling to make inroads with voters less than seven weeks before the election. Bowser, the poll found, holds a 17-point advantage.

Catania, an at-large council member since 1997, has clamored to debate for months on the belief that he can articulate a clearer vision for the city than Bowser, the council member for Ward 4. In scores of meet-and-greets with voters over the summer, Catania did not shy away from criticizing Bowser, calling her legislative record shallow and questioning whether she understands the intricacies of education policy and other responsibilities of the mayoralty.

But it wasn’t Catania, it turned out, who was first to lambaste Bowser.

As Bowser discussed her efforts as chair of the Council’s Government Operations Committee to pass an ethics reform package, she was interrupted by an audience member yelling, “Park Southern! Park Southern!” — a reference to the dilapidated Southeast Washington apartment building that has been a political thorn in Bowser’s side.

Catania quickly picked up the theme and criticized Bowser for merely assembling the proposals of others, saying that important campaign finance measures were “punted to a colleague.” He also criticized Bowser for delaying the move to an elected attorney general.

Bowser held her ground, saying the ethics board her bill established guarantees that allegations “couldn’t go into a black hole and die.” Schwartz, meanwhile, criticized Bowser and Catania for passing campaign finance reforms yet agreeing to an effective date after the pending election.

“Those loopholes are still wide open, and they are still driving their cars through those loopholes,” she said.

Bowser sought to parry Catania’s attacks with some attacks of her own — in one instance, making reference to Catania’s former job as a construction company executive.

Parents, she said, “want educators to run the schools; they don’t want M.C. Dean’s lawyer running the schools,” pursuing “untested, unproven” ideas that “may not have any impact on a child’s educational career.”

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Catania listened to the attack and smiled broadly, a regular pose for him throughout the debate. He launched into a defense of his aggressive approach to education reform, noting that he spoke to scores of educators before pursuing changes. “Ms. Bowser, you voted for every one of my measures,” he said. “Every last one!”

He also criticized Bowser’s legislative record on education, prompting a bout of cross talk, with audience members demanding “let her talk.” Ultimately, moderator Tom Sherwood, a WRC-TV (Channel 4) reporter, lectured the candidates, “It sounds like you need a class on behavior.”

The attacks held particular peril for Catania, whose reputation for confrontation appeared to register with voters in the Post/NBC poll. Bowser held a wide lead among likely voters asked which candidate has the best temperament to be mayor.

To combat Catania’s relative strength on vision and experience, Bowser attempted some political jujitsu, seeking to portray Catania’s recitation of his health-care record as the claims of a braggart.

After Catania described saving the bankrupt United Medical Center and working to lower the number of HIV/AIDS-related deaths, Bowser stood and turned to the crowd: “Mr. Catania has a very strange way of taking credit for everything,” she said. “Next thing you know, he’s going to take credit for the blue sky and the rolling seas. The fact of the matter is, no single person is responsible for the deep improvements in our health-care system.”

In their direct pitches to voters, Bowser cast herself as a listener and consensus builder; someone who can make life better for the “lives of every one in the District of Columbia”; Catania himself as the candidate with a proven record of improving city services from inside the belly of District government; and Schwartz herself as the experienced former council member who promised to return civility to the John A. Wilson Building.

Bowser has vulnerabilities, according to the poll. She earns the support of only half of likely Democratic voters and, since a March Washington Post poll asked voters about a Bowser-Catania matchup, she has lost support among registered Democrats, white voters, younger voters and female voters.

But Catania’s aggressive stance has apparently not helped him capi­tal­ize on Bowser’s weaknesses. His share of the electorate has barely budged. He has lost support among independents, and on the issue of education, which Catania has made the cornerstone of his campaign, he trails Bowser among likely voters, with 34 percent saying Bowser would do more for public schools to 28 percent for Catania and 17 for Schwartz.

After the debate, Catania took aim at the new polling. He said he trusted his internal polling, which surveyed a list of frequent voters rather than relying on respondents’ assertions that they intended to vote.

There were moments of comity. All said they agreed with efforts to craft as strict a law as possible to comply with a recent court ruling striking down the city’s ban on carrying firearms. Given a choice between riding a bike and using public transportation for the rest of their lives, all chose the latter. And rather than ask each other questions, both Bowser and Catania used their opportunity to quiz a fellow candidate to address Schwartz.

Catania asked Schwartz about a campaign debt, which she said did not exist, and Bowser asked her why she didn’t leave the Republican Party earlier. Being the only Republican on the D.C. Council, she replied, was “hurtful to me, but helpful for the city” by giving her credibility among national leaders.

Bowser tried, on one occasion, to raise the issue of Catania’s personality, when a panelist, Washington Post columnist Clinton Yates, asked Catania if he had visited Nationals Park — a project he had opposed as a council member. Catania said he hadn’t.

Catania’s refusal to visit the stadium five years after its opening, she said, “just kind of speaks to his temperament.” Her supporters in the crowd applauded, and Catania’s booed.

Catania smiled at the suggestion. “It had nothing to do with temperament; it had to do with the fact I wasn’t interested in going. . . . I do look forward to going to the stadium as mayor.”

Robert McCartney and Scott Clement contributed to this report.