The decision, announced Thursday on Twitter, means Mr. Booker has chosen a possible race against U.S. Sen. Frank R. Lautenberg, a fellow Democrat who is now 88, over one with Republican Gov. Chris Christie in 2013.
Mr. Booker’s announcement alters the landscape for both races, and for politics in Newark, the state’s largest city, where the mayor’s term runs through June 2014.
“Let there be no doubt, I will complete my full second term as mayor,” Mr. Booker said in a statement posted on Facebook. “As for my political future, I will explore the possibility of running for the United States Senate in 2014.”
It’s not clear whether Mr. Lautenberg will retire or run against Mr. Booker, and probably others, in a Democratic Senate primary at age 90. A Lautenberg spokesman was not immediately available for comment.
Mr. Booker reached out to Mr. Lautenberg on Thursday morning, but it’s not clear whether the two talked. Mr. Booker also made a round of calls to Democratic county political chairs and state Senate President Stephen Sweeney, another Democrat said to be considering a run for governor or another office.
“It will be a privilege, an honor, to continue his legacy of service,” Mr. Booker said of Mr. Lautenberg in a 3-minute video that accompanied his announcement. Mr. Booker, considered a rising star in the party, was not available for questions.
Mr. Lautenberg, known as the lawmaker behind the ban on smoking on airplanes, served three terms in the Senate before retiring in 2001, but he returned to politics less than two years later, taking the ballot spot of scandal-plagued Sen. Robert Torricelli. In 2008, Rep. Robert E. Andrews took him on in a primary election, but Mr. Lautenberg won with the support of much of the state’s Democratic Party establishment.
It gets touchier as he ages in part because the governor gets to decide who will complete an unexpired Senate term. As long as Mr. Christie remains in office, it’s likely a Republican would replace Mr. Lautenberg should he not be able to continue serving.
While New Jersey voters have alternated between Republican and Democratic governors for decades, the state is solidly blue when it comes to the U.S. Senate. The last time a Republican was elected to represent the state there was in 1972.
Many Democrats viewed Mr. Booker as having the best chance at unseating Mr. Christie. Just one prominent Democrat, state Sen. Barbara Buono of Metuchen, has announced a gubernatorial candidacy so far. Now that Mr. Booker’s out, the party will look for decisions from others, including Mr. Sweeney and state Sen. Dick Codey.
Ms. Buono on Thursday praised Mr. Booker’s work in Newark and made a play for support from Democrats who were waiting to see whether he might run for governor.
“With the mayor’s announcement today — and having already earned the endorsement of the Middlesex County and Somerset County Democratic Parties,” she said in a statement, “I am asking Democrats across New Jersey to join our campaign for the Democratic nomination for governor.”
Mr. Christie’s popularity is at an all-time high following his handling of Hurricane Sandy and its aftermath. In announcing his re-election bid last month, Mr. Christie said he was motivated, in part, by the chance to lead New Jersey through the post-storm recovery, which he said won’t be complete when his first term expires.
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