[2] He was a candidate for the Democratic presidential nomination in the 2020 election, launching his campaign on June 23, 2019, and ending it on December 1, 2019,[3][4] subsequently endorsing Amy Klobuchar.

In the Democratic primary he defeated incumbent Senator Arlen Specter, in office since 1981, 54% to 46%, but lost the general election to Republican nominee Pat Toomey in a close race.

[13] Sestak has also served as president of FIRST Global, a nonprofit with the objective of promoting STEM education that brought high-school age teams from 157 countries to Washington, D.C., for the inaugural robotics Olympics.

On August 30, 1991, Sestak took command of the guided missile frigate USS Samuel B. Roberts, which was named the Atlantic Fleet's best surface combatant in the 1993 Battenberg Cup competition.

[26] In 2005, Sestak pushed to add a second aircraft carrier in the Pacific to support allies, deter challenges from China, and be closer to potential hot spots such as the Koreas and the Taiwan Strait, saying, "if you don’t have the speed to get to the conflict when you really need to be there, you’re interesting, but irrelevant.

"[30] In an investigative report by The Philadelphia Inquirer, Chief of Naval Operations Vern Clark said of Sestak: He did what I asked him to do; I wanted straight talk, and this put him in the cross-hairs.

'"[32] Of Sestak's reassignment by Mullen, Clark told The New York Times, "I put him in that environment where he was in a position to create enemies," adding, "I should have given him better top cover.

Sestak first thought this meant his hometown's Delaware County Community College, but he was eventually steered toward the correct DCCC, the Democratic Congressional Campaign Committee, and informed its head, Rahm Emanuel, of his candidacy.

[36] Sestak decided to run anyway and turned to his brother, Richard, and sisters, Elizabeth and Margaret, who served as his campaign manager, top fundraiser and treasurer, respectively.

[38] Sestak received campaign donations from people around the world,[citation needed] including performer Jimmy Buffett, John Grisham, Bill and Hillary Clinton, and many Naval officers.

[41] The race remained a dead heat until late October, when FBI special agents raided the homes of Weldon's daughter and a close friend in connection with a federal corruption probe[42] (neither has ever been charged with a crime).

Most significantly, Sestak created the House Pediatric Cancer Caucus, which he co-chaired; extended benefits for those seeking work (COBRA) as a part of the JOBS bill; co-wrote the amendment to give small businesses tax credits, as a part of health care reform;[50] and moved the first significant federal funds into autism care and research, nicknamed the "Sestak Amendment".

Most prominent was a straw poll conducted by the Progressive Change Campaign Committee titled, "Should a Draft Sestak movement be created to take on Sen. Arlen Specter in the Pennsylvania Democratic primary?"

On May 27, 2009, Sestak indicated that he intended to challenge Specter in the 2010 Democratic primary (pending a final family decision because he had not "had the time to sit down with my eight-year-old daughter or my wife to make sure that we are all ready to get in").

[99] Republican Congressman Darrell Issa, the minority leader on the House Committee on Oversight and Government Reform, initially alleged that such an offer and Sestak's failure to report it could be felonies.

[100] Legal analysts disagreed,[101] and Issa subsequently backtracked and dismissed the issue; his spokesperson said, "it was a mistake",[102] and Issa said, "as we discovered, that it turns out that Republicans and previous administrations thought it was OK."[103] Specter held a 20-point lead in polls as late as April 2010, and enjoyed support from the Democratic establishment, including Rendell and Philadelphia Mayor Michael Nutter, with the latter trying to mobilize voters in that city for Specter.

Sestak attacked Specter's switch as "self-interested", and the move was disapproved of by a majority of registered Democrats in Pennsylvania, while a "fervent anti-incumbent mood" prevailed nationwide in the 2010 midterm elections.

After securing the Democratic Party's nomination, calling it "a win for the people, over the establishment, over the status quo, even over Washington, DC," Sestak enjoyed a slight lead in the polls against the Republican nominee, former Congressman and Club for Growth President Pat Toomey.

Toomey's effective fundraising and advertising allowed him to rise in the polls, at one point gaining a double-digit lead, causing political pundits to move the race from "Toss Up" to "Lean Republican".

[109] At the beginning of election night Sestak led in the exit polls by a wide margin, but as more votes were counted and central Pennsylvania's "red T" area began reporting, Toomey caught up.

After Citizens United v. Federal Election Commission was decided, conservative Political Action Committees and corporations broke the record for outside spending, airing ads on Toomey's behalf and causing Sestak to be outspent 3 to 1.

Previous recipients of the Bradley Chair include former Assistant Secretary of State Philip J. Crowley and retired Major General John D. Altenburg.

Sestak remained active in public service through the Center for Refugee and Disaster Response at the Johns Hopkins Bloomberg School of Public Health; the Ploughshares Fund working on nuclear disarmament; the Lenfest Foundation focused on education in Philadelphia, pre-K through early childhood, and those in danger of leaving or having left high school; co-chair with former Republican governor Mark Schweiker of the Pennsylvania State Advisory Committee of the U.S.

"[125][126] Sestak simultaneously published his vision in a policy-based book, Walking in Your Shoes to Restore the American Dream, co-authored with Jake Sternberger.

[139][140] The national Democrats' meddling in the primary was largely unpopular with their liberal base,[141] as Sestak consistently polled higher than McGinty in a hypothetical matchup against Toomey.

[170] In response, Sestak and other veterans argued that they should not punish soldiers for the President's actions, and supported the bill in order to give the armed forces adequate protection and equipment until withdrawn for the one year it would take to do it safely.

[171] Sestak supported the FISA Amendments Act of 2008, which critics contended continued the Bush administration's policy of warrantless wiretapping and provided retroactive immunity to telecommunications companies who participated in the National Security Agency's "terrorist surveillance program".

[175] In 2017, Sestak became the first president of FIRST Global, a nonprofit founded by Dean Kamen with the objective of promoting STEM education and careers in the developing world through Olympics-style robotics competitions.

Afghanistan's team made headlines when its visa requests were denied twice and it almost missed the competition, until President Donald Trump intervened to urge the State Department authorities to reconsider.

Sestak is married to the former Susan L. Clark, who works in international environmental issues from Kazakhstan to Mozambique; Russian relations, including the U.S. team searching for clues for Prisoners of War/Missing in Action within Soviet Union archives; and on suicide prevention for the Veterans Administration and Department of Defense.