Sen. Frank Lautenberg died this morning of viral pneumonia at age 89, his office said.
The oldest member of the Senate, Lautenberg had struggled with health problems since late last year, when he missed several weeks of votes because of what he said was flu and bronchitis.
The death of Lautenberg, a Democrat who was the longest-serving senator in New Jersey history, creates a vacancy that Governor Christie, a Republican, will fill.
Lautenberg returned to Washington in February and announced he would not seek re-election in 2014, but hoped to complete a series of accomplishments before his term ended. He had a breakthrough last month on one of them, a bill to overhaul the law that regulates chemicals used in household products, when a bipartisan compromise bill was unveiled.