WASHINGTON (AP) — U.S. Sen. Cory Booker on Friday declared his bid for the presidency in 2020 with a sweeping call to unite a deeply polarized nation around a "common purpose."

The New Jersey Democrat, who is the second black candidate in a primary field that's already historically diverse, delivered his message of unity amid an era marked by bitter political division. He announced his run on the first day of Black History Month, underscoring his consequential status as America's potential second black president after Barack Obama.

"I believe that we can build a country where no one is forgotten, no one is left behind; where parents can put food on the table; where there are good-paying jobs with good benefits in every neighborhood; where our criminal justice system keeps us safe, instead of shuffling more children into cages and coffins; where we see the faces of our leaders on television and feel pride, not shame," Booker said in a video message to supporters, subtly jabbing at President Donald Trump.

"It is not a matter of can we, it's a matter of do we have the collective will, the American will?" he added. "I believe we do."

Booker enters what's shaping up to be a crowded presidential primary, with three of his fellow Democratic senators — Elizabeth Warren of Massachusetts, Kamala Harris of California and Kirsten Gillibrand of New York — already either declared or exploring a run. But he's spent months telegraphing his intentions to join the race, visiting the early-voting states of Iowa, New Hampshire and South Carolina to build connections with key powerbrokers. He already has slated trips back to those states later this month.

Booker began reaching out to key constituencies Friday, conducting call-in interviews with three radio shows popular with black and Hispanic listeners. Later on Friday, Booker will be a guest on "The View," a TV talk show popular with female viewers, where his mother plans to sit in the audience.

A former mayor of Newark, New Jersey's largest city, Booker won a special Senate election in 2013 to replace Democrat Frank Lautenberg and then won a full Senate term in 2014. He will be able to run for a second full Senate term in 2020 while running for president, thanks to a law that New Jersey's governor signed in November.

But that doesn't mean the 49-year-old's path to the nomination will be easy. As many as five more Democratic senators could soon mount their own primary bids, creating a competition for voters' attention, and several of Booker's rival presidential hopefuls bring higher name recognition to a race that may also feature popular former Vice President Joe Biden.

The affable Booker, known for his fluency in connecting with voters during an age of selfies and social media, also could face some difficulty winning the hearts of the Democratic base due to his past financial ties to banking and pharmaceutical interests. Booker said he would stop taking contributions from pharmaceutical companies in 2017, the year that he partnered with potential presidential rival Sen. Bernie Sanders of Vermont on a bill that would allow importation of prescription drugs from Canada.

He also will likely stand alone as an unmarried candidate, though he brings a compelling personal biography that could help elevate his message that "the only way we can make change is when people come together."

Booker's father grew up in a low-income community in North Carolina, and the senator has recalled his family's later struggle to settle in suburban New Jersey amid discrimination against black homebuyers. The senator has brought a heartfelt and passionate style to his achievements in the Senate, at times fusing his personal spirituality with policy proposals that focus on social justice. Booker played a key role in the bipartisan criminal justice reform bill that Trump supported last year, for example, a deal he helped strike two months after sparring with Republicans during the battle over Supreme Court Justice Brett Kavanaugh's confirmation.

In his announcement video, Booker invoked the fight against slavery and the role of immigration in building the nation's character.

"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," he said.

Born in the nation's capital but raised in New Jersey, Booker made a name for himself as Newark mayor by personally shoveling the snow of residents. He has $4.1 million left in his campaign coffers that could also be used to assist his presidential run. Rather than opening an exploratory committee to test the waters, Booker took the direct step to open a campaign seeking the Democratic nomination.

Booker is aligning with many other prominent Democratic White House contenders by forswearing all donations from corporate political action committees and federal lobbyists to his campaign, dubbed Cory 2020. A prominent Booker supporter, San Francisco attorney Steve Phillips, says he is working on millions of dollars in committed donations to a so-called super PAC that would boost the senator's candidacy, but Booker's campaign is openly against super PACs playing any role in the presidential race.

Booker's campaign manager will be Addisu Demissie, who managed California Democratic Gov. Gavin Newsom's campaign last year and previously worked on Hillary Clinton's 2016 presidential bid. His deputy campaign manager, Jenna Lowenstein, is also a veteran of Clinton's 2016 campaign, while his current Senate chief of staff, Matt Klapper, will serve as a senior campaign adviser.

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