Former Pennsylvania congressman and retired three-star admiral Joe Sestak announced Sunday that he is running for president, becoming the 25th candidate to seek the Democratic nomination. Sestak, a Vietnam War veteran who also served in Iraq and Afghanistan, made his announcement in a video posted to his campaign website.

At his first campaign event in Waterloo, Iowa, Sestak told an audience of four caucus-goers that "Americans want someone they can trust."

"Americans want someone who is accountable to them above self, above party, and above any special interest," Sestak said. "They want a President that has a depth of global experience to restore U.S. leadership to the world and to protect our American dream at home."

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Sestak, who served in the Navy for more than 31 years, joins a historically crowded field of Democrats looking to take on President Trump in 2020. In a recent CBS News/YouGov poll of registered Democrats in early primary states, 71% said there are too many choices.

In his announcement video, Sestak explained he joined the race later than other candidates because his daughter was battling brain cancer. "The decision to delay was so I would be there with Alex, our daughter, as the brain cancer she courageously beaten at four years old returned this past year." He noted that his daughter "has again overcome the single-digit odds."

The retired admiral told reporters in Waterloo he plans to get his message out in the field of 24 other candidates "step by step." He added that voters "want to know if I know them, not if you just know me and the policies."

Sestak defeated 10-term Pennsylvania Republican Wayne Curtis Weldon in 2007 for a House seat and won reelection in 2009 in a traditionally red district. He said his daughter's initial battle against cancer inspired him to serve in the House "in order to work for all Americans to have health care coverage we fortunately had for Alex."

Sestak said he will work on having a public option for health care right away, but added millions of Americans have some form of private health care and cautioned against immediately eliminating private health insurance. He said he wants to see "a transition of choice," so that voters who prefer private insurance don't have to "change their health care plan in two to four years."

In this March 4, 2015, file photo, former Pennsylvania Rep. Joe Sestak smiles during a news conference in Philadelphia. AP

The former congressman touted his record as a Democrat in Pennsylvania's traditionally red 7th District while pushing for progressive policies like universal background checks for gun owners and supporting a woman's choice to reproductive health care.

While speaking to potential caucus-goers, Sestak highlighted his experience in national security and said that "an illiberal world order is beginning to emerge." He described the Trump administration's actions internationally as bordering isolationism and warned that America's "retreat from the world will lead to the contraction of the American dream."

Sestak, who commanded an aircraft carrier battle group that conducted combat operations in Afghanistan and Iraq, called the U.S. withdrawing from the Iran Nuclear Deal "embarrassing."

"We broke our word when Iran kept theirs," Sestak said. He also cautioned against launching air strikes on Iranian facilities and infrastructure.

"It will take us weeks if not months to destroy all of their air defense systems. This is not Iraq, this is a sophisticated air defense system where they have hundreds of missiles that can reign down on Israel, our regional bases, allies in the region, in the weeks it takes to find them and destroy them."

Sestak also spoke at length about China's growing influence in the world though its Belt and Road initiative. He said the program has left some countries "enslaved to China" because they can't pay off their debts.

He called climate change the "most catastrophic threat to America and the world," and added there is nothing the U.S "can do by ourselves" to solve the issue. Sestak warned that concerns of climate change could lead to "violent wars" due to lack of "diminished natural resources."

Sestak also ran for Senate in Pennsylvania in 2010 and 2016. In 2010, Sestak defeated Sen. Arlen Specter in the primary but lost to Republican Pat Toomey by two points in the general election. Six years later, he lost by 10 points in the primary to Katie McGinty, a former secretary of the Pennsylvania Department of Environmental Protection. McGinty lost to Toomey in the general election.