BOSTON (AP) — Steve Kerrigan, the 2014 Democratic nominee for lieutenant governor, is the latest candidate to jump into an increasingly crowded field hoping to succeed Democratic Rep. Niki Tsongas, who isn't seeking re-election.

Kerrigan is president of the Massachusetts Military Heroes Fund — a nonprofit supporting families of military personnel with ties to Massachusetts who have died as a result of active duty service since the Sept. 11, 2001 attacks.

Other Democratic candidates include Andover native and former aide to Boston Mayor Marty Walsh Dan Koh, Andover native and Cambridge City Councilor Nadeem Mazen, first-term state representative from Lawrence Juana Matias and Lori Trahan, a former aide to Marty Meehan when he was in Congress.

Republican candidates include Pepperell businessman Rick Green and Groton businessman and Iraq War veteran Scott Gunderson.