Newark Mayor Cory Booker leaves after a news conference discussing his plans to campaign for the Democratic nomination to run for the seat of late U.S. Sen. Frank Lautenberg on June 8, 2013 in Newark, New Jersey. New Jersey Governor Chris Christie has set October 16th as the date for a special election to determine who will fill Lautenberg's seat for a year. (Photo by Ramin Talaie/Getty Images)

The family of the late U.S. Sen. Frank Lautenberg of New Jersey has endorsed Rep. Frank Pallone in the race to choose Lautenberg’s successor, but Newark mayor Cory Booker remains the heavy favorite in the August 13 Democratic primary.

The written endorsement, attributed to “The family of Senator Frank R. Lautenberg,” takes several shots at Booker, who had a tense relationship with Lautenberg.

In praising Pallone, Lautenberg’s family emphasizes the next senator from New Jersey should “be a workhorse, not a showhorse” and “celebrity status won’t get you very far in the real battles that Democrats face in the future.”

Booker’s critics, including Lautenberg before he passed away, argue the mayor has spent more time building his national profile and Twitter following than in tending to the needs of Newark.

“Frank Pallone worked with Frank Lautenberg for many years.  He understands what it takes to take on and defeat Republicans and the special interests that attack the well being of working families.  While it may not always attract glamorous headlines, Frank knows that to be effective you must put New Jersey and your principles first, not your own glory,” the Lautenberg family wrote.

Booker, at a press conference Monday, emphasized that the endorsement of his rival was not a surprise, as Pallone and Lautenberg had long been allies. He strongly defends his tenure as mayor of Newark.

And the endorsement aside, the mayor is in very strong shape to  become the only black Democratic in the Senate.

A poll released by Quinnipiac University this week showed Booker with a huge lead in the race. According to the survey, Booker currently has 52 percent of the vote in the Democratic primary, compared to 10 percent for Pallone, 8 percent for Rush Holt, another Democratic congressman running for the seat and 3 percent for Assembly Speaker Sheila Oliver.

In a blue state like New Jersey, the winner of the Democratic primary will be a heavy favorite in the Oct. 13 general election.