Rep. Niki Tsongas (D-Mass.) will endorse Massachusetts Attorney General Martha Coakley tomorrow in the race to replace the late Ted Kennedy in the U.S. Senate. Tsongas is the widow of the late congressman and senator, Paul Tsongas.

Tsongas, in her first full term, was elected to the House in a 2007 special election. She is endorsing Coakley over fellow House member Michael Capuano, a Boston-area congressman in his sixth term in office. Capuano has won the endorsement of four other members of the state's House delegation.

The Coakley campaign announced that the endorsement event will take place tomorrow afternoon in Lowell, located in Tsongas's 5th Congressional District.