The powerful Democratic lawmaker is expected to announce her endorsement at Brown's Sunday campaign event in Silver Spring, according to three people with direct knowledge of the event.
Brown's campaign declined to confirm or deny the endorsement by Mikulski. Brown's campaign manager Justin Schall said, "We are very excited about Sunday, but you'll have to come to see who it is."
Brown, a Democrat now in his second term as lieutenant governor, has collected endorsements from more than half of Maryland's elected officials since he launched his campaign for governor this spring.
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