Newark Mayor Cory Booker announces his plans to run for the U.S. Senate seat formerly held by the late Frank Lautenberg. (EDUARDO MUNOZ/Reuters)

NEWARK — Newark Mayor Cory Booker, who formally declared his candidacy for U.S. Senate on Saturday, now finds himself competing against like-minded Democratic congressmen in a primary that will be decided in midsummer, when exceptionally low voter turnout threatens his early advantage.

Booker, 44, made his announcement at a news conference in Newark, New Jersey’s largest city, which he has led since 2006. He is vying to fill the seat of U.S. Senator Frank Lautenberg, who died Monday at age 89.

Gov. Chris Christie set the primary for Aug. 13 and a special election for the remainder of Lautenberg’s term for Oct. 16.

“We need someone in the United States Senate who’s actually had to work on difficult problems, who’s actually had to find people jobs, who’s actually had people standing in front of their homes and had to work on everything from getting people into food-stamp programs to helping young people better afford college,” Booker said Saturday. A second kickoff event was planned later in the day in the predominantly minority municipality of Willingboro in South Jersey.

Reps. Frank Pallone and Rush Holt are also planning to enter the Democratic primary, though neither has formally announced his candidacy. Candidates have until 4 p.m. Monday to file petitions with the secretary of state.

Booker started fundraising for a 2014 Senate campaign after announcing he would not run against Christie for governor. Currently, Pallone has more money banked — $3.7 million to Booker’s $1.9 million, as of the end of March.

But Booker has a national profile and a knack for getting public attention, from staging a hunger strike to protest drug-dealing to rescuing a woman from a burning home last year. Some critics complain that he has spent too much of his time burnishing his profile outside 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. Zuckerberg is planning to host a fundraiser for Booker’s Senate run soon.

Booker is considered the early front-runner, though election observers agree anything can happen in a hastily called summer election.

“It will be a question of who can get organizational support from county parties or labor — support from those who will knock on doors and get people out to vote,” said political analyst Patrick Murray of Monmouth University.

—Associated Press