Senator Frank Lautenberg made another dig about Newark Mayor Cory Booker, a likely challenger for his U.S. Senate seat in 2016

(Photo by Mark Wilson/Getty Images)

Describing Newark as a "city in desperate need of attention," the 89-year-old Senator told the National Journal that Booker has "got a lot of work to do -- a lot of work that should have been done  and hasn’t been done."

Booker made his intentions known in a video released just before Christmas and has filed with the Federal Election Commission. However, in the wake of anonymous comments made by Lautenberg aides calling Booker "disrespectful" and accusing him of stealing Lautenberg's ideas, Booker's run become less certain  when he told David Gregory on NBC's Meet The Press that it would be "premature" to say he will run.

Other potential Democrat candidates, disappointed that he passed on a run against Governor Chris Christie, have made veiled negative comments about Booker. Assembly Leader Sheila Oliver this week indicated she may be interested in Lautenberg's seat as well.

Lautenberg has not made his re-election plans known. “I know the people of New Jersey trust me,” he told the National Journal. “They’ve seen me hard at work constantly for now 28 years.”

However, a Quinnipiac University poll this week shows Booker leading Lautenberg 50-34% with a 50% job approval rating. But 45% responded that he does not deserve to be re-elected.

It's the second derogatory comment Lautenberg has made about Booker this week. He told the Philadelphia Inquirer of Booker's challenge, ""I have four children, I love each one of them. I can't tell you that one of them wasn't occasionally disrespectful, so I gave them a spanking and everything was OK."