The candidates touched on a variety of subjects affecting lower-income people. Mr. Sanders reiterated his call for voting rights for incarcerated people. Senator Kamala Harris of California, a former prosecutor, spoke of changing the cash bail system and providing relief to renters. Senator Elizabeth Warren of Massachusetts outlined her plan to create a wealth tax and use the proceeds to pay for programs like universal child care.

On the matter of how to deal with likely Republican opposition in the Senate, Ms. Warren went in a different direction than Mr. Biden. She repeated her call to get rid of the Senate filibuster if necessary, so that a narrow Democratic majority in that chamber could push through legislation over Republican objections.

“We have to be willing to get in this fight,” Ms. Warren said.

The Poor People’s Campaign is led by the Rev. Dr. William J. Barber II, a civil rights leader from North Carolina, and the Rev. Dr. Liz Theoharis, the director of Kairos: The Center for Religions, Rights and Social Justice at Union Theological Seminary in New York.

The issue of poverty is at the heart of the campaign. In 2017, about 40 million people in the United States were in poverty, or roughly 12 percent of the population, according to the Census Bureau. To show the scope of the issue, however, the campaign says that by another measure, some 140 million people can be considered either poor or low-income.

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“The word ‘poor’ has basically become a four-letter word for the past half a century,” Dr. Theoharis said in an interview. “If some politicians talk about it, it’s to punish and demonize people who are poor. And many, including many Democrats, refuse to even talk about the poor.”

The candidate forum was an effort to put a spotlight on the subject. “There has to be a narrative shift,” Dr. Barber said in an interview. “If we keep having an anemic, small, limited political debate and discussion, we’re going to keep getting what we’ve always gotten.”

Before the forum on Monday, the Poor People’s Campaign and the Institute for Policy Studies, a liberal think tank, released the Poor People’s Moral Budget, a lengthy collection of policy proposals intended to help establish a “moral economy.” The proposals included reducing military spending by nearly half and increasing taxes on corporations and wealthy people, including creating a wealth tax that mirrors what Ms. Warren has proposed.

Organizers of the forum said Mr. Trump was invited to appear but did not respond. The Trump campaign declined to comment.