Booker has announced his intention to seek Lautenberg's seat in 2014. The incumbent New Jersey senator will be 90 years old if he decided to mount a reelection bid rather than retire. But the swipe Thursday night is another signal that Lautenberg is upset with Booker's decision to publicly declare his intention to challenge the long-term lawmaker.
Still, Booker is heavily favored to take the Democratic nomination if Lautenberg decides to seek reelection. In a Quinnipiac University poll released earlier this week, Booker held a 51-30 percent lead among primary voters. More than seven in 10 say Lautenberg's age makes his work too difficult.