New Jersey Sen. Cory Booker launched his candidacy for the Democratic presidential nomination on Friday, telling supporters he wants to be a uniting force in an increasingly divided country.

“We are better when we help each other,” the former Newark mayor said in a video emailed to supporters and released on Twitter, where he has 4.1 million followers.

“I believe we can build a country where no one is forgotten, no one is left behind. … Together, we will channel our common pain back into our common purpose. Together, America, we will rise,” he said.

A senator since 2013, Booker enters an already crowded Democratic field that is sure to get even more jammed. Candidates who have already announced bids or exploratory committees include Sens. Elizabeth Warren of Massachusetts, Kirsten Gillibrand of New York and Kamala Harris of California; Rep. Tulsi Gabbard of Hawaii; former Rep. John Delaney of Maryland; South Bend, Indiana, Mayor Pete Buttigieg; and former Housing and Urban Development Secretary Julián Castro.

Booker’s announcement was expected: He’s traveled the country over the past two years, campaigning for Democrats in more than two dozen states, including early-voting Iowa and New Hampshire and perennial battlegrounds Florida, Michigan, Ohio and Wisconsin.

The trips helped him bank favors with candidates and build his brand with party regulars as he posed for endless selfies and delivered fiery speeches at party fundraising dinners. The executive director of Virginia’s state Democratic Party told NorthJersey.com in June that only Barack Obama and Hillary Clinton drew more people than Booker to the party’s annual dinner.

Also watch: ‘You can’t lead the people if you don’t love the people,’ Booker says

With the help of others, Booker notched a partial victory on one of his top priorities in the Senate in December when President Donald Trump signed a bill to roll back mandatory minimum prison sentences for some drug crimes and allow those sentenced under old laws to file for release.

Other priorities include environmental justice, which is a commitment to ensuring the poor aren’t subjected to pollution. Booker cited that issue in signing on to the proposed “Green New Deal,” advocated by freshman Democratic Rep. Alexandria Ocasio-Cortez of New York.

But Booker’s celebrity also made him a target of attacks and ridicule, especially after he compared himself to the Thracian gladiator Spartacus after fellow Democrats came to his support at a confirmation hearing last year for Supreme Court nominee Brett Kavanaugh. A conservative group’s call for Booker to face discipline from the Senate Ethics Committee for releasing confidential Kavanaugh emails was dismissed in Dec. 12.

While he apparently sees it as a selling point, Booker’s response to attacks could disappoint Democrats looking for a nominee to be as aggressive as President Donald Trump.

After Booker delivered a speech to the 2016 Democratic National Convention that, like Friday’s video, also featured “We will rise” as a rallying call, Trump tweeted that Democrats have no future if they turn to Booker because “I know more about Cory than he knows about himself.”

Asked about veiled threat on CNN, Booker said, “ I love Donald Trump. I don’t want to answer his hate with hate. I’m going to answer it with love. I’m not going to answer his darkness with darkness. I love him. I know his kids, I know his family. They’re good, the children especially, good people.”

Booker does not mention Trump by name in his 2½-minute video announcement Friday. But a list of changes he said he wanted to work to build concluded with wanting a country “where we see the faces of our leaders on television and feel pride, not shame.”

Trump’s tweet could have been a reference to Booker being single, a rarity for presidential nominees in the modern era. Asked about that and some opponents’ attempts in the past to use his status to question his sexuality, Booker told The Philadelphia Inquirer in December, “I’m heterosexual.”

Booker, 49, is the son of IBM executives who, with the help of fair housing activists, broke the race barrier to buy a home in an upscale North Jersey suburb. He frequently describes himself and his brother growing up as “a couple raisins in a tub of vanilla ice cream.”

Booker planned to follow up his video announcement, apparently timed for the start of Black History Month, by calling in to broadcasts aimed at black and Latino audiences. Later Friday, he planned to appear on ABC’s “The View,” with his mother in the audience.

An all-American football player in high school, Booker passed up Notre Dame and Duke to take a scholarship to play at Stanford. After graduating, he went Oxford University as a Rhodes Scholar and then got a law degree from Yale before moving into public housing in one of Newark’s poorest neighborhoods to work as a community activist.

After winning a seat on the city council, he challenged a veteran mayor who was one of the state’s most powerful Democrats. Booker lost, but a documentary about the campaign was nominated for an Academy Award, and Booker became a darling of liberal celebrities, especially after he easily won the next mayoral race.

Booker’s rise to the top of New Jersey politics was partly due to his ability to attract support from celebrities and Wall Street financiers with deep pockets.

But it also had a downside. As a surrogate speaker for Obama’s 2012 campaign, Booker had to walk back remarks he made on Meet the Press when he used the word “nauseating” to describe Democratic attacks on Republican nominee Mitt Romney’s work at a venture capital firm.

In recent years, Booker has worked to bolster his credentials with the party’s most liberal wing.

He unveiled a plan to combat income inequality that would have the government put up to $1,000 in a savings account for every child when they are born and supplement it with annual payments of up to $2,000. He also co-sponsored a bill with Warren, Gillibrand, Harris and Sen. Bernie Sanders of Vermont that would make everyone eligible for Medicare.

Elected to a one-year unexpired term following the death of Sen. Frank R. Lautenberg in 2013 and re-elected in 2014, Booker’s Senate term is up in 2020. New Jersey changed its election laws in November allowing someone to run on state ballots for both senator and president.