In the wake of primaries in US Senate and state Senate races, and a general election for a state Senate seat, Dorchester and Mattapan voters will go to the polls next week for the third time in three months. This time, on June 25, it’ll be to choose John Kerry’s successor.

US Rep. Ed Markey, a Malden Democrat, and newcomer Gabriel Gomez, a Cohasset Republican, are the two candidates on the ballot, survivors of the April 30 primary that winnowed the fields on either side.

The public’s interest in the special election – set in motion in December when Kerry was tapped as President Obama’s chief diplomat – has been sluggish by most accounts.

Voter listlessness was on display on Sunday at Roxbury Community College where the candidates faced off in a forum put together by MassVOTE and other groups. About 70 people trickled into the college’s media arts auditorium to watch Markey and Gomez hammer away at each other. The candidates took turns bristling as they exchanged well-honed talking points peppered with references to the “American Dream.”

One of the issues they differed on is the federal Affordable Care Act, modeled on the Bay State’s health care law. “I would not repeal Obamacare,” Markey said. “Mr. Gomez would. He says he would. I just think that there’s a reason why that’s my proudest vote in my Congressional career. Because I think it goes right to the heart of health care justice.”

For his part, Gomez said, “What the Affordable Care Act’s going to do, it’s going to make it more expensive for you to have health care. And it’s very simple why. We have our own health care right here since 2004 with a program. But now we’re going to have to subsidize the other 49 states that didn’t have the great health care program we had here in Massachusetts.”

Polls have consistently shown Markey with a lead, including a Boston Globe poll – released on June 16, the day of the forum – that put Markey up by 13 points. But Democrats remain cautious, and John Walsh, the state’s party chairman, has asked several mayoral campaigns in Boston to focus on the Markey-Gomez battle in its last days.

State Rep. Marty Walsh, a Dorchester Democrat running for mayor, said he is suspending his campaign between June 20 and June 25 because he wants “our canvassers, phone bankers, data people and other staff out there working day and night” for Markey.

Bill Walczak, a fellow Dorchester Democrat who is also running for mayor, said he would also suspend his campaign. “When the Markey campaign contacted us several weeks ago with this request, we agreed without hesitation,” Walczak said in a statement. “My colleagues and I may not agree on who the next mayor of Boston should be, but we all agree that Ed Markey should be the next senator from Massachusetts. We will suspend other field activities to focus on this effort.”

At the Roxbury forum, Gomez arrived early and made awkward small talk in the auditorium’s basement with the forum’s moderator, Karen Holmes Ward of WCVB-TV (Channel 5).

When Holmes Ward approvingly noted that it seemed like the Republican Party was diversifying – a reference to Gomez’s Colombian roots – Gomez said, “We’re moving right along.”

Gomez cited Bill Weld and the late Paul Cellucci, two Massachusetts governors who were considered moderate Republicans, as role models. Then, pointing to right-wing talk show hosts like Howie Carr, Gomez said, “They think I’m a Democrat already.”

Once inside the auditorium, Gomez began working the room, shaking hands and greeting audience members. But as the clock ticked on and the small crowd waited for Markey to enter, the Republican appeared to run out of hands to shake. At one point, Gomez walked up an empty aisle and looked up at several of his staffers in the auditorium’s last row. “Woo! Gomez!” one of them said, softly and with a smile.

“Start the wave,” Gomez quipped, half-raising his arms above his head.