Mayor Bill de Blasio Thursday huddled inside Gracie Mansion with a dozen progressive leaders from around the country and brainstormed ways to promote their agenda at all levels of American politics.

De Blasio said that next month, the group would release a list defining its program in the mold of then-Rep. Newt Gingrich's 1994 "Contract with America" -- the campaign platform credited with helping Republicans retake both houses of Congress that year -- except this one will promote left-of-center policies.

"All of this is focused on the notion that we are not having the discussion of income inequality in this country, and we are not having that discussion at our peril," de Blasio said after emerging from the private session with his wife, Chirlane McCray, and members of the group to address reporters.

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The session marked another pivot to a stage beyond the five boroughs for de Blasio.

In September, he addressed a British Labour Party conference in Manchester, England. This month, he plans to travel to Iowa -- which will be center stage next January for the 2016 presidential race -- as well as Nebraska and Wisconsin.

His efforts have not always been successful: Last year, he spent political capital to help Democrats retake the State Senate, but Republicans emerged from Election Day in full control of the chamber.

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De Blasio said Thursday that the staff of Hillary Rodham Clinton -- the all-but-declared front-runner for the Democratic nomination -- was not involved in the discussions.

"She's not a candidate yet. If she becomes a candidate, I absolutely believe she needs to address this issue. I think all leaders and all candidates need to address this issue," said de Blasio, who managed Clinton's successful 2000 U.S. Senate bid.

McCray, whom de Blasio calls his most important political adviser, said, "I feel as though the prayers of poor people, working people, people of good conscience everywhere are being answered by the beginning of this very public conversation that we've needed to have in this country for a long time."

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The attendees included Sen. Sherrod Brown (D-Ohio), Connecticut Gov. Dannel Malloy, author Toni Morrison, The Nation magazine's Katrina vanden Heuvel, and environmental activist Van Jones.

"This is a national hero," Jones said of de Blasio. "There are very few leaders in this country that have the stature to call the kind of meeting this man called."

Sen. Elizabeth Warren (D-Mass.), a leading progressive voice, could not attend because of a scheduling conflict, a de Blasio spokeswoman said.