MJ Hegar, the Air Force veteran who narrowly lost a 2018 House bid against Rep. John Carter John Rice CarterDonna Imam wins Democratic runoff to face Rep. John Carter House panel advances bill banning construction on bases with Confederate names Democrats see victory in Trump culture war MORE (R-Texas), announced Tuesday that she will challenge Sen. John Cornyn John CornynThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight Senate GOP faces pivotal moment on pick for Supreme Court MORE (R-Texas) for his seat in 2020.

“Texans deserve a senator who represents our values: strength, courage, independence, putting Texas first,” Hegar said in a video announcing her Senate bid that included a cameo appearance by comedian Patton Oswalt.

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Hegar’s entrance into the race sets up the potential for a bruising Democratic primary.

Rep. Joaquin Castro Joaquin CastroFlorida Democrat asks FBI to investigate anti-Semitic, racist disinformation Hispanic Caucus members embark on 'virtual bus tour' with Biden campaign Hispanic caucus report takes stock of accomplishments with eye toward 2021 MORE (D-Texas) is also seriously considering a Senate run in 2020, and, like Hegar, has prominent Democrats backing him.

Democrats have long eyed Texas as a potential battleground, pointing to signs that the longtime reliably red state has begun to trend toward flipping to blue in recent years.

President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE carried the state by 9 points in 2016, down from Mitt Romney Willard (Mitt) Mitt RomneyBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power The Memo: Trump's strengths complicate election picture MORE’s nearly 16-point win in 2012.

Former Rep. Beto O’Rourke’s (D-Texas) 2-point loss to Sen. Ted Cruz Rafael (Ted) Edward CruzCruz blocks amended resolution honoring Ginsburg over language about her dying wish Trump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP MORE (R-Texas) last year energized the Democratic Party even further, prompting them to set their sights on Cornyn, the former Senate majority whip.

Hegar’s Senate announcement has been in the works for weeks.

After O’Rourke, who is now running for the Democratic presidential nomination, announced that he would not mount a bid for Senate in 2020, Hegar met with Senate Minority Leader Charles Schumer Chuck SchumerCruz blocks amended resolution honoring Ginsburg over language about her dying wish Senate Democrats introduce legislation to probe politicization of pandemic response Schumer interrupted during live briefing by heckler: 'Stop lying to the people' MORE (D-N.Y.), a strong sign that she was considering a challenge to Cornyn.

And just this week, Hegar posted a since-deleted tweet that included a photo of Cornyn’s Senate office.

Hegar became a top-tier contender for the Senate after she came within 3 points of ousting Carter in Texas's 31st District last year — a district that Trump carried by nearly 13 points in 2016.

Republicans immediately took aim at Hegar, denouncing her as Schumer’s hand-picked candidate.

“New York liberal Chuck Schumer Chuck SchumerCruz blocks amended resolution honoring Ginsburg over language about her dying wish Senate Democrats introduce legislation to probe politicization of pandemic response Schumer interrupted during live briefing by heckler: 'Stop lying to the people' MORE found his chosen candidate in MJ Hegar,” Jesse Hunt, a spokesman for the National Republican Senatorial Committee, said. “Hollywood Hegar’s support for late-term abortion and government-run health care will play better with progressive Hollywood celebrities than with mainstream Texans.”

Cornyn’s campaign manager, John Jackson, suggested that Hegar’s announcement was a sign that Schumer had managed to shut down Castro’s Senate ambitions.

“It appears Chuck Schumer was able to push Joaquin Castro out of the race, and we’ll see if he has the same success with Councilwoman Edwards,” he said, referring to Amanda Edwards, a Houston city council member who is also considering a run for the Senate seat.

--Updated at 10:49 a.m.