U.S. Sen. Frank Lautenberg, D-N.J., announced Thursday that at age 89, this will be his last term. He will not seek re-election in 2014, leaving the seat open for a battle among ambitious Newark Mayor Cory Booker and other New Jersey politicians.

“I am not announcing the end of anything. I am announcing the beginning of a two-year mission to pass new gun safety laws, protect children from toxic chemicals and create more opportunities for working families in New Jersey,” Lautenberg told The Star-Ledger of Newark. “While I may not be seeking re-election, there is plenty of work to do before the end of this term and I'm going to keep fighting as hard as ever for the people of New Jersey in the U.S. Senate.”

Lautenberg, a businessman who was already well into middle age when first elected to the Senate in 1982, has been one of the Senate's most stalwart liberal voices over his three-decade career, which was interrupted when he retired in 2000 but came back two years later to save the seat for the Democrats. 

Recently, he has been a leader in pushing to renew a lapsed ban on assault weapons and restricting the size of ammunition magazines, The Star-Ledger notes. He has been one of the biggest supporters of Amtrak and other mass transit (and has a train station named after him), and battled the tobacco industry for years, leading the effort to ban smoking on domestic airplane flights. He also sponsored a bill to withhold federal funds from states that did not raise their drinking age to 21, and helped rewrite hazardous waste cleanup law.

Several polls showed Lautenberg trailing Booker in a 2014 primary, but the senator’s aides were miffed that Booker openly announced his intentions before Lautenberg made a decision about his retirement first.

"Senator Frank Lautenberg has been a champion for the people of New Jersey for decades and his legacy of service will improve the lives of all American's for years to come," Booker said Thursday, according to The Star-Ledger.

"Frank is a steadfast champion of the people of New Jersey," said President Barack Obama. "Throughout his time in the Senate, Frank has fought tirelessly for workers, veterans, members of our military and their families, and immigrants, and he continues to make extraordinary contributions to our nation's safety, and the health and welfare of our citizens. His service in World War II is a testament to his character and deep commitment to public service."

"Frank Lautenberg and I have had our differences through the years, but I've always respected him for his tenacity, devotion to the people of New Jersey and his love for and commitment to public service," said Republican Gov. Chris Christie.

Booker may be the leading Democratic candidate for the seat, but he will not be unchallenged. Rep. Frank Pallone, D-N.J., has told party leaders he will run if Lautenberg retires, and Assembly Speaker Sheila Oliver and Senate President Stephen Sweeney may run as well.

New Jersey has not elected a Republican U.S. senator since 1972.