Maryland Sen. Jamie Raskin (D) in 2010. (Ricky Carioti/THE WASHINGTON POST)

Updated at 6 p.m. with remarks from event

State Sen. Jamie B. Raskin (D-Montgomery) formally announced his candidacy Sunday for the Maryland 8th Congressional District seat being vacated by Rep. Chris Van Hollen (D).

Raskin, 52, who represents Takoma Park and Silver Spring in the state Senate, is the second Democrat to officially enter what is expected to be a closely contested race. Del. Kumar P. Barve (D-Montgomery) announced his candidacy last month.

Van Hollen is running to succeed the retiring Sen. Barbara A. Mikulski (D).

Speaking to supporters who packed Republic restaurant in Takoma Park for his kickoff, Raskin said he was running to bring new ideas and and progressive values to Congress.

“My ambition is not to be in the political center. My ambition is to be in the moral center,” said Raskin, who was unopposed in his election to a third term in Annapolis last year.

Raskin, the son of Marcus Raskin, a prominent liberal activist and National Security Council staff member in the Kennedy White House, cited his leading role in floor fights for social and environmental legislation, including the Green Maryland Act, the marriage equality law and the repeal of the death penalty. He vowed to pursue the same agenda on Capitol Hill.

“I’m not afraid to take on the deadlock and dysfunction in Washington,” he said.

The Democratic primary field is expected to grow. Others who have expressed interest in the race include Dels. Ana Sol Gutierrez, Ariana B. Kelly and Jeffrey D. Waldstreicher; Marriott executive Kathleen Matthews; and former Montgomery County Council member Valerie Ervin.

Businessman and former state senate candidate Frank Howard is the lone Republican to publicly express interest.