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STORY: CRUMP: "What happened on Saturday was an act of domestic terrorism."

After the massacre at a Buffalo supermarket that left ten people dead, police said authorities were examining a 180-page manifesto that suspected gunman Payton Gendron appears to have written and posted that outlined the so-called "Great Replacement Theory."

CRUMP: "You think about this race replacement theory, that he talked about in this manifesto. There are people who are pushing this hatred on these young people, indoctrinating their minds to go out and commit violence."

Civil rights attorney Benjamin Crump appeared with victims' families on Monday and pointed his finger at unnamed politicians for spreading this dangerous myth.

CRUMP: "It's these people who are accomplices to this mass murder."

ROSENTHAL: "Replacement theory is the idea that white populations, both in North America, here in the U.S.A., and in Europe are being replaced by minority populations, largely through immigration."

Lawrence Rosenthal leads the Berkeley Center for Right-Wing Studies.

He said replacement theory inspired deadly white supremacist attacks in a Pittsburgh synagogue, an El Paso Walmart, and a Christchurch mosque, where gunmen attacked groups they believed threatened the future of the white race.

ROSENTHAL: "They all cite replacement theory as the theoretical basis behind what they're doing."

But another version of replacement theory has crept from neo-Nazi manifestos into more mainstream politics. Some U.S. Republicans and right-wing media figures suggest without evidence that the Democratic party is trying to bring an influx of immigration to the U.S., change the electorate, and take political power.

Implicit in this theory is the idea that immigrants and other minorities tend to vote Democratic, whereas white voters lean Republican.

ROSENTHAL: "There is a way in which the implications, and the hints, and the allusions to replacement theory are abroad in the whole spectrum of the Republican right these days."

U.S. Representative Liz Cheney on Monday blamed her fellow Republicans for failing to stop the replacement rhetoric, tweeting, "The House GOP leadership has enabled white nationalism, white supremacy, and anti-semitism.

House Republican conference chair Elise Stefanik, herself accused of pushing replacement ideas, pushed back, calling the allegation "a new disgusting low."

While investigators say racism motivated the Buffalo attack, Crump on Monday said those who spread racist lies also needed to be held accountable.

CRUMP: "They may not have pulled the trigger, but they loaded the gun."