The 44-year-old Democrat made his candidacy official at a news conference Saturday in Newark, New Jersey's largest city. He was joined by former U.S. Sen. Bill Bradley, who for 18 years held the seat Booker is seeking.
Bradley, who endorsed Booker, called him "the right person for the right office at the right time."
Booker began raising money for a Senate run even before Lautenberg, who died Monday, announced retirement plans in February. He had raised $1.9 million by the end of the last reporting period in March.
Reps. Frank Pallone and Rush Holt are also planning to enter the Democratic primary. Booker is considered the early front-runner.
Pallone, 61, had $3.7 million in his campaign coffers at the end of March and has deep union support. Holt, 64, a former research physicist, had $800,000 on hand.
Gov. Chris Christie, a Republican, announced this week that there would be party primaries Aug. 13 and a special general election Oct. 16
The only Republican running so far is Steve Lonegan, a former Bogota mayor who runs the New Jersey office of Americans for Prosperity.
Booker, 44, has 1.4 million followers on Twitter – or five for every resident of the city where he's the mayor. He tweets frequently, answering questions about city services, posting about his workouts and, perhaps most often, trying to provide inspiration.
He's frequently gotten public attention, from staging a hunger strike to protest drug-dealing to rescuing a woman from a burning home last year. His life story is also captivating. He grew up in Harrington Park as the son of civil rights activists who were among the first black executives at IBM, went to Stanford, was a Rhodes Scholar, earned a law degree from Yale and took a job with the Urban Justice Center, which provides legal and other services to the vulnerable. He also moved to a public housing complex in Newark.
Booker started fundraising for a 2014 Senate campaign after announcing he would not run against Christie for governor, citing his desire to finish his term in Newark. The term expires in June 2014, meaning if he wins the Senate election he'll go back on his word.
Booker's critics in Newark see him as an ambitious interloper who spends too much of his time outside the city.
According to a Senate campaign filing made in May, Booker has brought in $1.3 million for 90 speeches he has given around the country since 2008. His campaign says he has donated the majority of that money to charities that serve Newark.
Booker's campaign has said that the networking he does ultimately helps the city.
In 2010, he was seated next to Facebook founder Mark Zuckerberg at a dinner during a conference in Sun Valley, Idaho. Two months later, Zuckerberg announced a $100 million donation to improve education in Newark.
[let's not forget how he used Twitter to help his constituents after Sandy. honestly surprised they didn't mention that!]
source bets NJ residents and Booker fans will be cheering
mods, i'm surprised we don't have a Senate tag? also can we get the tag someone suggested awhile back? i believe it was "this looks like a job for Cory Booker". thanks.