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“Amazingly, in a down economy, Newark is in its biggest period of economic growth since the 1950s,” he said.

Despite the development and philanthropic money, Newark’s unemployment rate stands at about 15 percent, and the city continues to rely on the state to help balance the budget. The City Council did not pass the 2012 budget until October. The state lent Newark $32 million last year, and it ended up with an $18 million surplus. So this year, Christie slashed the aid by $22 million, chiding the administration for how it handled the budget.

Mr. Booker has 1.3 million Twitter followers and is known for responding to constituent complaints sent to him electronically. During superstorm Sandy, he invited residents to charge their cellphones at his house. In April, he let the world know through Twitter that he rushed into his neighbor’s house and rescued her from a fire. And during a snowstorm, he helped shovel people out.

He was elected mayor of Newark in 2006 with 72 percent of the vote, four years after narrowly losing a bruising battle against longtime Mayor Sharpe James. The race was chronicled in the 2005 documentary “Street Fight.” He was re-elected in 2010 with about 60 percent of the vote

A Stanford-educated Rhodes Scholar who grew up in suburban Harrington Park, N.J., Mr. Booker is the son of civil rights activists who were among the first black executives at IBM. He got his law degree from Yale Law School, then moved to one of Newark’s most notoriously violent housing projects.

• Associated Press writer Katie Zezima in Newark contributed to this report.