TRENTON, N.J. —  Sen. Frank Lautenberg is running for office again.

The 84-year-old Democrat will announce his re-election bid Monday afternoon. Several partisan pals — including Gov. Jon Corzine — are expected to be on hand.

Lautenberg has been raising money for another run for at least a year. The Federal Election Commission shows he had $4.3 million cash on hand as of Dec. 31, and has already spent about $750,000.

He's unchallenged in the primary so far, though former Gov. Brendan Byrne's son Tom Byrne says he will decide within a day or so whether to run.

At least three Republicans have declared their candidacy.