New Jersey Senator Cory Booker is officially running for president.

He made the announcement on Friday morning, becoming the fourth U.S. senator to enter the historically crowded Democratic primary field. In a campaign video released on Twitter, Booker emphasized his commitment to economic and racial justice, as well as his record as mayor of Newark prior to joining the senate in 2013.

"Over 20 years ago I moved into the central ward of Newark to fight slumlords and help families stay in their homes," Booker said. "I still live there today, and I'm the only senator who goes home to a low-income, inner-city community."

As part of his campaign roll-out, Booker, 49, is set to appear on The View later today. He's also spoken with a trio of radio shows—all of them led by black or Latino hosts—and highlighted that his announcement was pegged to the first day of Black History Month.

"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 wrote in an email to supporters on Friday morning.

Booker, who's long articulated an optimistic vision of politics, seems to have found a growing audience for his message of partisan unity under President Trump. He's considered a serious contender for the nomination, and has been laying the groundwork for a run for several months—making his first trip to Iowa back in October.

Booker is expected to return to the state next week, and will head to South Carolina on February 10th, according to CNN. Over Presidents Day, he intends to visit New Hampshire, whose state Democratic Party chair has called Booker “the best friend New Hampshire Democrats had in 2018.”

But as he's built fervent support from many Democrats, Booker has attracted criticism from the progressive wing of the party, who point to his moderate record and ties to Wall Street as nonstarters. As mayor of Newark, he famously called Obama's attacks on private equity "nauseating," even as his own conservation and development corporation was, according to the Times, "pilfering from Newark."

More recently, he rejected a proposal aimed at lowering prescription drug prices, earning him accusations of "doing the industry’s bidding." He also has an extensive track record of supporting charter schools—putting him closer to Secretary of Education Betsy DeVos than most Democrats on the issue.

Though he faces re-election to the senate in 2020, Booker won't be forced to take himself off the ballot. In November, New Jersey Governor Phil Murphy signed a bill—dubbed "Cory's Law"—allowing a senator or member of the house to seek both offices at the same.

In addition to Booker, Kirsten Gillibrand, Elizabeth Warren, Kamala Harris, Tulsi Gabbard and Pete Buttigieg have formally announced their runs for presidency, while both Bernie Sanders and former Starbucks CEO Howard Schultz say they’re “looking” at running. Joe Biden has also said he’s not ruling out a run.