Former Rep. Joe Sestak, D-Pa., became the latest Democrat to challenge President Trump’s seat in the Oval Office when he declared on Sunday he's running for president.

Sestak, a retired Navy admiral who represented Pennsylvania’s 7th District from 2007 to 2011, becomes the 25th candidate among the primary field of Democrats.

"What Americans most want today is someone who is accountable to them, above self, above party, above any special interest... a president who has the depth of global experience to restore America’s leadership in the world to protect our American Dream at home... and one who is trusted to restructure policies where too many see only the growth of inequity not of the economy," Sestak said in a video released on his campaign website.

He added: “I want to be that president who serves the American people the way they deserve to be served.”

Sestak acknowledged he was entering the race both as a latecomer in an already crowded field and as an underdog compared to big names such as former Vice President Joe Biden and Sens. Bernie Sanders, Elizabeth Warren, Kamala Harris and Cory Booker. He also would be absent from the stage in the Democrats' first debates this week.

The former congressman said his reason for announcing his White House bid now was that he'd been supporting his daughter in her fight against brain cancer.

“[M]y announcement may be later than others for the honor of seeking the presidency. The decision to delay was so I would be there with Alex, our daughter, as the brain cancer she had courageously beaten at four years old returned this past year,” he said. “But, with her same team of medical heroes, she has again overcome the single-digit odds.”

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In his relatively short campaign announcement, Sestak laid out two main objectives he wanted to tackle: battling climate change and “putting an end to an illiberal world order’s injustices, from China’s control of the 5G network to Russian interference in democratic elections.”

During his time in Congress, Sestak chafed many top Democrats for challenging longtime incumbents. He twice ran – and lost – for one of Pennsylvania’s Senate seats.

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In 2009, he launched a primary challenge to then-Sen. Arlen Specter, who had switched parties to run as a Democrat. Despite efforts by the Obama White House and other top Democrats to get him to bail out of the race, Sestak refused – ultimately beating Specter in the primary in 2010, but losing to Republican Pat Toomey in the general election.

Sestak launched another Senate bid in 2016 but lost in the primary to former Pennsylvania Environmental Protection Secretary Katie McGinty, who received an endorsement from then-President Obama and a large infusion of cash from outside liberal groups. McGinty ultimately lost to Toomey in the general election.