Sen. Jeffrey Chiesa of New Jersey is the Senate's newest member but he shouldn't get too used to his surroundings - he'll only be there for four months.

The Republican was sworn-in Monday in a ceremony led by Vice President Joe Biden. GOP Gov. Chris Christie appointed Chiesa, his state's attorney general, to the seat last week after longtime Democratic Sen. Frank Lautenberg's death.

Chiesa will be the interim senator until an Oct. 16 special election determines who will take Lautenberg's spot. Chiesa says he will not run in the special election to complete the term, which expires in January 2015. Chiesa is the first Republican senator from New Jersey since another fill-in back in 1982.

With Chiesa's arrival, the Senate has 52 Democrats, 46 Republicans and two independents who often vote with the Democrats.

The Associated Press contributed to this report.