Rep. Chris Van Hollen scored a major endorsement Thursday in the Maryland Democratic Senate primary, winning the backing of state Del. Maggie McIntosh (D).

McIntosh, a longtime Baltimore politician who chairs the Appropriations Committee in the Maryland House of Delegates, called Van Hollen "one of the most effective leaders that we have in Maryland." McIntosh spoke from a popular diner in Baltimore, where she introduced the congressman to several patrons.

The two worked together in Annapolis, where Van Hollen served for 12 years before becoming a congressman.

"Maggie McIntosh is one of the most important political figures in the state," said Vinnie DeMarco, a longtime public health lobbyist and Van Hollen supporter. "This endorsement means a lot."

McIntosh is a close friend of retiring Sen. Barbara A. Mikulski (D), who does not plan to endorse a candidate and says she would like to see a competitive race. Van Hollen faces Rep. Donna Edwards of Prince George's County in the primary to replace Mikulski; Reps. Elijah Cummings and Dutch Ruppersberger of Baltimore are still considering bids.

"She knows what I'm up to today," McIntosh said of Mikulski. She agreed that many Baltimore politicians were not ready to endorse while Cummings, a veteran inner-city legislator, is still a potential candidate.

"I think ... there are a lot of people in Baltimore City that have worked with Chris and feel exactly the way I do, and in due time they will speak for themselves," she said. "I began to think, why wait?"

At the press conference, Van Hollen said that later in the day he would announce his position on President Obama's nuclear deal with Iran. Edwards has repeatedly criticized her fellow congressman for not backing the agreement earlier, as she did. In a statement, Edwards's spokesman argued that Van Hollen was "flirt[ing] with the same position as Donald Trump and Ted Cruz."

Van Hollen said he wanted his decision to be put in context, saying that those Republicans had rejected the deal in a "knee-jerk fashion."