PHOENIX — Arizona Republican Martha McSally accused her Democratic opponent Kyrsten Sinema of once advocating for "treason" on Monday, calling out her rival's old comments during the pair's sole debate to fill the state's open Senate seat.

"You said it was okay for Americans to join the Taliban to fight against us," McSally said, raising her voice and pointing emphatically at Sinema, who stood about 10 feet away, as the debate neared its conclusion, referencing a 2003 radio interview. "I will ask right now whether you're going to apologize to the veterans and me for saying it is okay — it is treason!"

Sinema responded: "Martha has chosen to run a campaign like the one you're seeing right now. She’s engaging in ridiculous attacks and smearing our campaign." After the debate, she told reporters that the claims she had supported Americans fighting with the Taliban were "ridiculous."

The 2003 radio interview surfaced in a report by CNN over the weekend in which Sinema, a leader of anti-war efforts in Phoenix in the early 2000s, dismissively answered a probing question by a Libertarian radio host. She said: "Fine. I don't care if you want to do that, go ahead."

McSally doubled down in comments to reporters after the debate.

"I was taking shots at the Taliban when I was flying the A-10 Warthog," said McSally, a former fighter pilot who was stationed in Saudi Arabia with the Air Force in 2003. "This is the definition of treason, saying it's okay for Americans to join our enemies. They're responsible for 3,000 people dying on 9/11, and thousands of soldiers afterwards, and you think that’s okay? And she wouldn’t even apologize to us for that?"

Polls show the race in a dead heat.

The two candidates debated a range of issues, from healthcare to the Supreme Court and immigration, before the debate turned contentious in its waning minutes.

"While we were in harm's way, she was protesting our troops in a pink tutu," McSally said, calling Sinema's anti-war protests and past comments "disqualifying."

Sinema countered that she would not be an "apologist" for her party or a president if she were to serve in the Senate.

"I think we deserve a senator who calls the balls and strikes," Sinema said.

McSally would not say whether she voted for Donald Trump in the 2016 election but will campaign alongside him at a rally on Friday in Mesa.

The two congresswomen are vying for the seat of Republican Sen. Jeff Flake, who is retiring. The Arizona Senate seat of the late John McCain is filled by appointee Jon Kyl until a 2020 election.

McSally is a former combat fighter pilot who was a Trump critic in 2016 and represents a Tucson district that voted for Hillary Clinton.

Sinema represents a district based in the Phoenix suburb of Tempe and is a former Green Party activist who transformed herself into a centrist Democrat. She has one of the most conservative voting records among Democrats in Congress and presents herself as a nonpartisan problem-solver.

Both congresswomen engaged in attacks Monday night as they have throughout the race, Democrats and Sinema have hammered McSally for voting to weaken protections for people with preexisting conditions and for shifting to the right on immigration. McSally dismissed those charges as "lies" Monday as she tried to steer the conversation back to Sinema's old anti-war activism.

Sinema contrasted her own voting record with McSally's, saying her rival was a blind partisan who voted 98 percent of the time with Trump. Sinema says she was willing to buck party leaders and back the president when he was right, but oppose him when he was wrong, citing a 60 percent voting record with the president.

Citing Sinema's support for Trump, McSally scoffed: "60 percent with the agenda is a failing grade in every school."

Trump won Arizona in 2016 but only by three percentage points and Democrats hope Sinema can appeal to enough disaffected Republicans to turn the normally red-leaning state blue in November. McSally spent the debate trying to goad Republicans into voting with their party and reject Sinema.

"The economy is doing great and Arizonans feel it every day," McSally said, crediting unified GOP control of government.

The two also tangled on the perennial Arizona issue of immigration. McSally supports Trump's border wall and slammed Sinema for not voting for two immigration bills that would have built it earlier this year. Both were only supported by Republicans but couldn't muster enough support to pass the House because some members of the GOP voted against them.

Sinema said "there was no bipartisanship in any of this discussion" and noted she voted to stiffen penalties against some people in the country illegally who commit crimes, which has angered members of her party.