Tony Bennett delivers remarks as Rep. Elijah Cummings, Chris Rock, the Rev. Timothy Boggs, Amanda Peet and Rep. Mike Thompson listen. (Paul J. Richards/ AFP/Getty Images)

One in an occasional series on the stars with a cause who come to Washington. Wednesday’s visitors: Chris Rock, Tony Bennett and Amanda Peet.

Setting: The Capitol Visitor’s Center.

Event: A press conference by Mayors Against Illegal Guns’ “Demand a Plan” campaign on gun violence.

Backup: Rep. Mike Thompson, chair of the congressional Gun Violence Prevention Task Force; writer/artist Anna Deavere Smith; RFK’s daughter Kerry Kennedy; Martin Luther King III; shooting victims and other advocates.

Chris Rock at the press conference. (Ann Heisenfelt/AP)

What they want: Congress to support President Obama’s plan — universal background checks, a ban on assault rifles and high-capacity magazines, more research money on gun violence.

How they sounded: Earnest, heartfelt. “I still haven’t gotten over Connecticut,” said Bennett. Peet acknowledged the proposals can’t stop all gun violence — “but what’s the alternative? Doing nothing will fail. Doing nothing has failed.”

Motives: Why does any celebrity wade into such complex, divisive territory? “Can’t hurt,” Rock told us. “When the ship goes down, you want to at least be able to say you were on the right side.” Bennett said he’s a pacifist — doesn’t like any guns. Peet’s sister and brother-in-law are doctors who treat shooting victims. (Rock and Peet, along with several other celebrities, appear in a new video supporting “Demand A Plan.”)

Soundbite: “The president and the first lady are kind of like the mom and the dad of the country,” Rock said. “When your dad says something, you listen. And when you don’t, it usually bites you in the a-- later on.”

Read more about celebvocates. . .

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