So as Ms. Edwards was greeting voters Tuesday night, Mr. Van Hollen was at a restaurant across town, mingling with an enthusiastic, and racially mixed, group of supporters over a dinner of chicken and mashed potatoes. Older black women cooed over him. His host, a Baltimore County councilwoman, Cathy Bevins, who is white, said she had just sent Emily’s List “a nasty little email, telling them, ‘Take me off your list.’ ”

The congressman, doing his best to avoid race and gender questions, reminded the crowd that he has Baltimore ties (his father grew up here) and of his attention to constituent service. He stiffened slightly when asked if the Senate needs a black woman’s voice.

Those who endorsed him, he said, can speak for themselves: “They want somebody with a track record of delivering real results.”

There has not been a black woman in the Senate since Carol Moseley Braun, the nation’s first and only black female senator, left in 1999. In California, Emily’s List is also backing Kamala Harris, who is black and Asian-American, for a Senate seat this year. Here in Maryland, a Monmouth University poll released on Thursday showed Mr. Van Hollen pulling ahead in what has been a tight race with voters, especially women, and starkly divided along racial lines.

“This is the state that Harriet Tubman ran away from twice and Frederick Douglass ran away from at least once, and we’ve never had a black woman elected statewide,” said Benjamin Jealous, the former president and chief executive of the N.A.A.C.P., who supports Ms. Edwards, though he insisted it was for policy reasons, not her race.

Maryland, a heavily Democratic state, is no stranger to rough primary campaigns, especially when there is a rare open seat. Ms. Mikulski, a gruff former social worker from East Baltimore, ran one herself 30 years ago. Then a congresswoman, she reached the Senate by beating a seasoned colleague, Michael D. Barnes, and a sitting governor, Harry Hughes, with the help of a new group: Emily’s List.