On Monday night, Republican Rep. Martha McSally and her Democratic opponent, Rep. Kyrsten Sinema, took to the stage for their first and only debate in the contentious race to fill the Senate seat being vacated by Jeff Flake. The debate grew heated, and one of the two candidates took her attacks to a new level when McSally accused Sinema of literal treason.

That accusation, leveled by McSally in place of answering a question about climate change, hinged on 2003 comments Sinema made in a radio interview while promoting an anti-war protest, as reported by CNN last week. According to CNN, in February 2003, while Sinema was an activist with ties to the Green Party, she was working to support an anti-war protest in Patriots Square Park in Phoenix. A local libertarian activist named Ernest Hancock invited her on his radio show and launched into a somewhat confusing set of hypothetical questions, one of which had to do with joining the Taliban.

“Now you would say, maybe we do owe something to the world, as long as it’s nice and sweet and peaceful and what you want to do,” Hancock said.

“Well it’s not so much a candy-cane kind of theory as you’re making it stand out,” Sinema said. “But I do think that those of us who are privileged to have more do owe something to others.”

“By force?” Hancock asked. “By me, as an individual, if I want to go fight in the Taliban army, I go over there and I’m fighting for the Taliban. I’m saying that’s a personal decision … ”

“Fine,” Sinema said. “I don’t care if you want to do that. Go ahead.”

A spokeswoman for the campaign told CNN that her interjection was “clearly offhand and an effort to get back on the topic of why she opposed the war.”

In the debate, McSally, a former Air Force colonel, repeatedly asked Sinema to apologize for that comment 15 years ago, depicting the comments as Sinema saying “it was OK for Americans to join the Taliban to fight against us.” She did not leave the implication unstated: “Kyrsten, I want to ask right now whether you’re going to apologize to the veterans and me for saying it’s OK to commit treason?”

When Sinema tried to reply, McSally said again, “It’s treason.”

Later, her campaign doubled down and circulated a statement with the definition of treason.

McSally, like many candidates who had to fight for her party’s nomination, became more Trump-like in her brand of conservatism during her campaign. Sinema, who has spent about 14 years as an Arizona legislator, is running on her record in the House of Representatives, and she has portrayed herself as pro-military. In response, Republican groups are highlighting her past progressive activism and opposition to the wars in Iraq and Afghanistan. Sinema has called McSally’s line of attack in Monday’s debate “ridiculous” and a smear effort.