When a white man used a semi-automatic assault-style rifle to kill 10 people at a supermarket in a Black neighborhood of Buffalo, New York, last weekend, attention quickly turned to the likely motive.
The "great replacement" theory describes a supposed elite conspiracy to change the demographics of America, replacing and disempowering white people - and their influence - with people of color, immigrants and Muslims. In recent years the lie has gone from far-right fringe to Republican party mainstream.
But anyone hoping that Buffalo would break the fever looks set to be disappointed. On the contrary, critics say, Republicans will probably intensify their racist rhetoric to prey on fears and energise supporters for the midterm elections, increasing the likelihood of more Buffalo-style violence.
"It's good for raising money and good for agitating the base that is already stressed and strapped by inflation and economic concerns and other social changes that they don't like," said Michael Steele, the first African American chairman of the Republican National Committee. "It's exploitive and it's going to result in more harm to African Americans and other minority communities."
Payton Gendron, 18, was jailed without bail on a charge of first-degree murder after police said he opened fire last Saturday at a Tops Friendly Markets outlet in Buffalo. Investigators are studying Gendron's online postings, which include a 180-page manifesto that outlines replacement theory.
During a visit to the crime scene on Tuesday, Joe Biden warned of "a hate that through the media and politics, the internet, has radicalised angry, alienated, lost and isolated individuals into falsely believing that they will be replaced - that's the word, 'replaced' - by the 'other' - by people who don't look like them and who are therefore, in a perverse ideology that they possess and being fed, lesser beings".
The president said he condemns "those who spread the lie for power, political gain, and for profit" and described silence as "complicity". Yet Republicans did remain mostly silent. The Senate Republican leader, Mitch McConnell, was asked about replacement theory three times on Tuesday but failed to provide a direct answer.
Steele commented: "I don't see them changing course. It works for their purposes. The leadership has not come out and condemned it. They refuse to acknowledge any link or nexus between that and the obvious evidence of that connection presented by the killer in Buffalo and so they try to continue to turn a blind eye to it."
Hate crimes and domestic terrorism are on the rise in the US. A white man who gunned down 23 people in El Paso, Texas, claimed that he was enraged by "the Hispanic invasion of Texas". A white man who killed 11 worshippers at a synagogue in Pittsburgh accused Jews of allowing immigrant "invaders" into the country.
In recent years various iterations of the theory, straining to avoid overt racism or antisemitism, have been articulated by Republicans at congressional hearings and in election campaigns. They have been amplified by rightwing media and given the ultimate platform by Donald Trump at the White House.
Elise Stefanik, the Republican chairwoman in the House of Representatives and a staunch Trump supporter, has been condemned for a Facebook ad last September that accused Democrats of trying to "overthrow our current electorate" through amnesty and enabling non-citizens to vote. Her office has denied any link to replacement theory.
Ron Johnson, a senator for Wisconsin, has described replacement theory as "the Democrat grand plan". He said in a radio interview last month: "I've got to believe they want to change the makeup of the electorate."
In the Trump era, Republicans evidently see no political incentive in distancing themselves from replacement theory. In an opinion poll released last week, the Associated Press-NORC Center for Public Affairs Research found that about one in three Americans believes that an effort is under way to replace US-born Americans with immigrants for electoral gain.
Several Republican Senate candidates are drawing on replacement theory as they campaign for November's midterm elections. In Ohio, Trump-endorsed JD Vance told the conservative Fox News network that Democrats "have decided that they can't win re-election in 2024 unless they bring a large number of new voters to replace the voters that are already here".
In Missouri, the Senate candidate Eric Schmitt, the current state attorney general, said Democrats are "fundamentally trying to change this country through illegal immigration". And in Arizona, which borders Mexico, another Senate candidate, Blake Masters, accused Democrats of trying to flood the nation with millions of immigrants "to change the demographics of our country".
The message now sits naturally in a party moulded by Trump, who promised to build a border wall, demonised illegal immigrants and hired "alt-right" figures such as Steve Bannon. His campaign slogan, "Make America Great Again" (Maga), was widely seen as a nostalgic nod to a simpler, whiter time.
Mark Takano, a Democratic congressman and vice-chair of the Congressional Asian Pacific American Caucus, said: "They need to take ownership of the fact that Trumpism is a cancer. Maga Republicans are a cancer on this republic."
"It is an already energised portion of the base and for them to pour water on this fire seems to them like a huge loss. It will be a huge loss for many of them to stamp it out. But they have to have faith that they will arise out of those ashes, that it's not worth the power they think they will attain by allowing themselves to take advantage of this very potent fire."
At a press conference on the steps of the US Capitol on Thursday, leading Democrats urged their Republican colleagues to join in the condemnation of replacement theory before it inspires another deadly attack.
Joyce Beatty, chair of the Congressional Black Caucus, described replacement theory as "a key plank of the Republican platform", adding: "Time and time again, domestic terrorists are using the great replacement theory to justify their crimes.
"Right here on Capitol Hill, we hear our Republican colleagues echoing versions of this theory. We must confront it. Let me say it in very clear terms: the Republican leadership is not innocent and, whether they use a dog whistle or a bullhorn, they do not get a pass."
Fox News's most watched host, Tucker Carlson, has been one of the theory's biggest proponents. A study of five years' worth of Carlson's show by the New York Times newspaper found 400 instances in which he talked about Democratic politicians and others seeking to force demographic change through immigration.
Kurt Bardella, an adviser to the Democratic National Committee and former senior adviser for Republicans on the House oversight committee, said: "Any time that you devote airtime to espouse these extreme viewpoints you are lending it legitimacy and normalising it and telling your audience that this is an acceptable viewpoint that deserves to be aired in the public domain. That's exactly what Fox News has done and they have blood on their hands."