TRENTON, N.J. – Cory Booker, once mayor of New Jersey’s largest city and now one of the most high-profile, media savvy U.S. senators, declared his candidacy for president Friday, joining an already crowded field of Democrats looking to be President Trump’s 2020 challenger.

Booker announced his long-anticipated decision the same way many Americans have come to know him, on Twitter, presenting himself as a healer of the country’s deep divisions and stressing the importance of “collective action.”

“I believe that we can build a country where no one is forgotten, no one is left behind,” Booker, 49, told his supporters in a rousing, 2-minute-and-25-second video. “It is not a matter of can we, it's a matter of do we have the collective will, the American will? I believe we do.”

Coming to prominence as mayor of Newark, then becoming New Jersey’s first African-American senator after winning a special election in 2013 to fill the remainder of the late Sen. Frank Lautenberg's term, Booker can point to a record of backing liberal policies, from marriage equality and abortion rights to marijuana legalization and criminal-justice reform.

In December, Booker was central to a bipartisan effort to pass historic changes to tough-on-crime prison and sentencing laws that then gained Trump’s signature.

But Democrats are wary of Booker’s ties to Wall Street and the pharmaceutical industry, relationships Booker has tried to downplay in recent months by, for example, renouncing contributions from corporate PACs but ones that could hurt him among progressive voters.

Booker at one point was the top recipient of Wall Street money in Congress and, in 2017, voted against a proposal aimed at lowering prescription drug prices, earning him the ire of many in his own party.

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Booker joins a diverse field of candidates that probably will swell into one of the most crowded primary contests in Democratic Party history.

Sen. Elizabeth Warren, 69, announced in December she was forming an exploratory committee, the first step a presidential hopeful takes before formally declaring. The two-term Massachusetts senator came into the national spotlight for her passionate criticism of Wall Street, the banking industry and large corporations after the 2008 financial crisis.

Two other prominent senators, Kirsten Gillibrand of New York and Kamala Harris of California, launched campaigns soon thereafter.

Other candidates include Hawaii Rep. Tulsi Gabbard, Maryland Rep. John Delaney, former San Antonio Mayor Julian Castro and South Bend, Indiana, Mayor Pete Buttigieg.

Booker’s first day on the campaign trail is expected to start with three call-in interviews on morning radio and TV programs and then an in-person appearance on ABC’s "The View."

Later Friday, Booker is scheduled to hold a news conference outside his home in Newark’s Central Ward, where he has lived for more than 20 years, first as a councilman and then as mayor for two terms.

In the video announcing his candidacy, Booker recounts his family’s experience breaking the race barrier to buy a home in the New Jersey suburb where he grew up, Harrington Park, and credited that move with setting the stage for the rest of his life — from high school football star to scholarship athlete at Stanford, followed by a Rhodes scholarship, a Yale law degree and his political career.

Booker frames his move to Newark as a way to pay forward the sacrifices made by his parents and notes that he is the only senator who goes home to a “low-income inner-city community.”

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Over archival footage of soldiers marching into battle that blend into images of modern-day protests, Booker intones that “we are better when we help each other.”

“The history of our nation is defined by collective action, by interwoven destinies of slaves and abolitionists, of those born here and those who chose America as home, of those who took up arms to defend our country, and those who linked arms to challenge and change it,” Booker says.

“Together, we will channel our common pain back into our common purpose,” he adds. “Together, America, we will rise.”

Follow Nicholas Pugliese on Twitter: @nickpugz