New Jersey Democratic Sen. Frank Lautenberg plans to retire, declining to seek reelection in 2014 in the face of a likely challenge from charismatic Newark Mayor Cory Booker. 

The 89-year-old lawmaker is the last remaining veteran of World War II in the Senate and has been elected easily five times. Lautenberg is a staunch advocate of gun control and public infrastructure and is a champion of the Amtrak railroad. 

But the expected challenge from Booker, who earlier was thought to be weighing a run for governor, meant Lautenberg would have been in for a tough primary battle. 

Lautenberg first won election to the Senate in 1982.

The Associated Press contributed to this report.