“When we talk about online radicalization we always talk about Muslims. But the radicalization of white men online is at astronomical levels,” the journalist Siyanda Mohutsiwa, who said she has been following the so-called “alt-right” forums on Reddit for years, wrote in a Twitter thread earlier this week. “These online groups found young white men at their most vulnerable & convinced them liberals were colluding to destroy white Western manhood.”

Groups that oppose immigration and political correctness, such as neo-Nazis, white nationalists, and the “alt-right,” have bloomed online in recent years. (It’s worth noting that these groups consider themselves distinct, and most don’t use the term “racist;” at most, they prefer the term “racialist.”) A study published in September by George Washington University extremism researcher J.M. Berger found “major American white nationalist movements on Twitter added about 22,000 followers since 2012, an increase of about 600 percent.” Berger found that people who followed white nationalists on Twitter referenced Trump “more than almost any other topic.”

The Nazi and white nationalist accounts in Berger’s sample rarely tweeted about Mitt Romney in 2012, but this year, “three of the top 10 hashtags for both white nationalist and Nazi datasets were related to ... Trump: #trump, #trump2016, and #makeamericagreatagain,” Berger wrote. The most common hashtag was “whitegenocide;” Trump retweeted a user with WhiteGenocide in his username in January.

(Trump’s campaign said the tweet wasn’t related to his personal views. In response to past stories about their white-power supporters, the campaign has said, “We have rejected and rebuked any groups and individuals associated with a message of hate and will continue to do so.”)

It’s impossible to tell how many people were motivated by racism to vote for Trump, who used anti-immigrant rhetoric and, occasionally, white-nationalist memes, all while telling black Americans he would “be your greatest champion.” Other issues, like abortion, the economy, and dissatisfaction with Obamacare also turned out Trump voters. But some Trump supporters were energized by concerns that people of color are somehow overrunning the nation, spreading violence and sucking up precious resources. Eight of 10 people who favor the deportation of illegal immigrants voted for Trump, according to exit polls, and Trump also performed better among voters who said their top issue was immigration or terrorism.

Early on, Republicans who felt white Americans were under threat preferred Trump to his rivals. In a Pew survey in April, those who felt it was “bad for the country” that in 30 years the U.S. will consist mostly of people of color were more likely to feel warmly toward Trump, as were those who felt Islam is violent. Other issues—homosexuality, family values, or economic fairness—didn’t polarize Republicans similarly.