Police say the threat may have come from the Bloods street gang, the New York Times reported. State police, the Essex County prosecutor and the county sheriff have been cooperating to ensure Booker's safety.
"There is some credibility to this," Sheriff Armando Fontoura said. "Whether it's maximum credibility or minimum credibility, it was prudent to take the action we took."
Mayor Sharpe James, who leaves office July 1 after running the city for 20 years, gave a hint of remaining bitterness when he said Booker had made the "unusual" request for his political supporters in his security detail.
Booker, a lawyer and former Rhodes Scholar, almost beat James four years ago in a nasty election documented in the movie "Street Fight." James decided not to seek a sixth term this year, apparently fearing he would be defeated, and Booker won in a landslide.