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In a Texas congressional district that includes one of the country's largest military bases, a military hero is betting she can stage a political upset.

Air Force veteran MJ Hegar is launching a Democratic challenge against U.S. Rep. John Carter, R-Round Rock, in Texas' solidly red 31st Congressional District.

"I see a threat to our Constitution, our democracy," Hegar said in a recent interview, "and I feel compelled to do something more about it."

Hegar served three tours in Afghanistan as a search-and-rescue pilot, and in 2009, she saved the lives of her passengers after her medevac helicopter was shot down by the Taliban. She subsequently received the Purple Heart as well as the Distinguished Flying Cross with Valor Device.

She went on to become a fierce advocate for women in the military, helping lead a 2012 lawsuit against the Defense Department over its now-repealed policy excluding women from ground combat positions.

Hegar's memoir, "Shoot Like a Girl: One Woman’s Dramatic Fight in Afghanistan and on the Home Front," was published earlier this year and is being made into a film. Angelina Jolie is reportedly in talks to star in it.

Carter's district has been reliably Republican, but Hegar, now an executive coach and consultant living in Round Rock, believes she can flip it, confident in her ability to garner crossover support with her experience at the national and international levels. She said her decision to run was partly motivated by the election of President Donald Trump, who has caused concern among even his own party's national security professionals.

"I think being a Republican is not what it used to be," Hegar said. "Even though [the district] is historically Republican, I think some people are voting Republican because they have a misperception of what the Democratic Party is."

Hegar grew up in a Republican family and voted for the party in her youth. But she said many of the things that once drew her to the GOP — including the principle of small government — are "no longer true," and she now describes herself as an "independent Democrat."

On a number of hot-button issues, Hegar strikes a moderate tone.

“I am for the Second Amendment, but I am for common-sense gun legislation," said Hegar, who said her household contains five firearms. "We take responsibility for being firearm owners. We take responsibility for whose hands those guns get into."

First elected in 2002, Carter has always beaten Democratic challengers by wide margins, including by 22 percentage points last year. He is a member of the powerful Appropriations Committee, a perch he has used to push for more defense funding. The CD-31 includes part of Fort Hood.

Referring to Carter as an "incumbent bystander," Hegar said she wants to send the message that lawmakers like Carter "cannot get away with just representing his voters, his special interests."

National Democrats are currently targeting three Republican incumbents in Texas that party leaders view as vulnerable: U.S. Reps. John Culberson of Houston, Will Hurd of Helotes and Pete Sessions of Dallas. Carter is not on that list, but Hegar is urging them to pay attention.

"Please look closer," she said her message is to groups like the Democratic Congressional Campaign Committee.

As she has prepared for the launch of her campaign, Hegar has been in touch with Democratic heavyweights such as Roy Spence, the Austin-based advertising legend who has worked on Hillary Clinton's presidential campaigns. Hegar could also be in a position to earn the support of EMILY's List, an influential national group that backs female Democratic candidates who support abortion rights.

Hegar is joining an already crowded field of Democrats who have filed to challenge Carter, including fellow veteran Kent Lester; Dr. Christine Eady Mann, a family physician in Cedar Park; and Mike Clark, who first challenged Carter in 2016. Hegar said she believes she has a "better chance to beat Carter than they do" — she cited her record, as well as her fundraising ability — "but I hope they continue to stay engaged."

Disclosure: Roy Spence has been a financial supporter of The Texas Tribune. Find a full list of donors and sponsors here.