By David Madden and Diana Rocco

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TRENTON, N.J. (CBS) –-  New Jersey governor Chris Christie has turned to a longtime colleague to serve as the interim replacement in the US Senate for the late Frank Lautenberg.

New Jersey attorney general Jeffrey Chiesea, who worked with Christie in the US attorney’s office before becoming the top lawyer for the state government, won’t seek the office in an October election to fill the seat, Christie said.

Chiesa, who will take the oath of office on Monday, says his legislative priority list is, for now, short:

“I think the first thing we have to do is to make sure the borders are secure.  I think that’s probably because I come from a background in law enforcement.”

Christie says he has known Chiesa for more than two decades so the choice wasn’t that difficult.

“I’ve appointed someone that I have great faith and confidence in, and someone who I know almost  as well as I know my own family,” the governor said today in Trenton.

Chiesa, a Republican, was Christie’s chief counsel until he was nominated in December 2011 to be attorney general.

As for that election, hopefuls have till Monday afternoon to file nominating petitions.  Christie will name an interim replacement for Chiesa’s attorney general post next week, and says the door is open if Chiesa wants to return to Trenton after his four-month stint in Washington.

Christie has scheduled a special election for October to fill the Lautenberg seat until it expires in January 2015. Whoever wins in October would have to run again in the fall of 2014.

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Lautenberg served nearly 30 years in the US Senate. The liberal Democrat was 89.

Earlier today, US Rep. Rush Holt became the first Democrat to announce he’s seeking his party’s nomination.

In an e-mail to supporters he explained why he’s running.

“The reason is simple,” he wrote. “I believe I am the best candidate to continue the passionate advocacy for progressive values that Sen. Lautenberg exemplified.”

Holt, now 64, was assistant director of the Princeton Plasma Physics Laboratory for most of the 1990s before being elected to Congress in 1998.  Around his central New Jersey district, it’s not uncommon to see a bumper sticker that proclaims, accurately: “My congressman IS a rocket scientist.”

He’s considered one of the most liberal members of New Jersey’s congressional delegation.  He’s pushed for laws against racial profiling and has been critical of drilling for oil and natural gas on public lands and waters.

Two well-funded Democrats, US Rep. Frank Pallone and Newark mayor Cory Booker, had expressed interest in the seat before Lautenberg died, but neither has made an announcement so far.  Booker began raising money to seek the seat in January and has brought in about $2 million.

The only Republican in the race so far is former Bogota, NJ mayor Steve Lonegan, a conservative who has twice sought his party’s nomination for governor.

Lonegan, who runs the New Jersey office for American for Prosperity, said Wednesday that he looks forward to weighing in on national issues such as the Obama administration’s handling of the attack last year at the diplomatic mission in Benghazi, Libya, and the selective scrutiny of conservative groups’ nonprofit tax applications.

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