Richard Spencer, a leading promoter of white nationalism, is hosting a major gathering Saturday that is expected to draw protesters. (Linda Davidson/The Washington Post)

A white nationalist organization that has come under fire for promoting racism will host a conference Saturday at the Ronald Reagan Building and International Trade Center in downtown Washington — a gathering of more than 250 that will celebrate Donald Trump’s presidential victory.

“The past 12 months might be remembered as the year of Donald Trump . . . and the year of the Alt Right,” according to the website for the National Policy Institute, which is hosting the event. “It was a time when more people joined our movement then [sic] ever before and when our ideas began invading the mainstream.”

The conference is expected to draw dozens if not hundreds of protesters, who have launched a Facebook page asking that people join them “to defeat this hate.”

The institute’s president, Richard Spencer, who coined the term “alt-right,” is a leading promoter of white identity. He and his followers oppose immigration and multiculturalism.

Friday night as prospective attendees of the Saturday conference gathered at a restaurant for a private dinner, protesters rushed up a flight of stairs toward them. They were prevented from reaching them, however, and went back outside to continue protesting.

About 200 people protested a gathering of white nationalists sponsored by the National Policy Institute at the Ronald Reagan Building and International Trade Center on Nov. 19 in downtown Washington. (Facebook/Tauhid Chappell)

The Southern Poverty Law Center describes the National Policy Institute as an extreme right-wing group whose core belief “is that ‘white identity’ is under attack by multicultural forces using ‘political correctness’ and ‘social justice’ to undermine white people and ‘their’ civilization.”

[What’s the alt-right? A primer]

The movement gained national prominence during the 2016 presidential campaign as supporters crusaded on Twitter and Facebook for Trump, whose blunt talk and immigrant bashing resonated with them.

When the president-elect named as chief White House strategist the former Breitbart News chief Stephen K. Bannon — who is closely associated with the movement — the alt-right’s leadership touted the appointment as another enormous victory for their cause.

“ ‘Strategist’ is the best possible position for Steve Bannon in the Trump White House,” Spencer wrote on Twitter, just days before the social media platform, without explanation, suspended him and a number of like-minded users.

Saturday’s speaker lineup features a number of prominent, and controversial, white nationalists, including Kevin MacDonald, a retired professor of psychology at the California State University at Long Beach, who is considered deeply anti-Semitic by Jewish groups. He is, the SPLC says, “the neo-Nazi movement’s favorite academic.”

Peter Brimelow, an author and anti-immigration activist who leads the VDare Foundation, will also address the gathering.

Spencer, a 38-year-old with degrees from the universities of Virginia and Chicago, has worked for months to inject the movement’s ideology into the mainstream, offering interviews to dozens of major media publications.

Although people have fiercely objected to the Reagan building hosting Saturday’s conference, the management has said it can’t discriminate because the building is federal.

On its Facebook page, the anti-fascist group “Smash Racism DC” celebrated that the Hamilton had canceled a Friday-night dinner the institute intended to host at the restaurant.

“We didn’t really know the nature of the event,” said Hamilton spokeswoman Molly Quigley. “Once there was a threat of protest and disruption, we canceled it for the safety of our guests and employees and our business.”

The restaurant, she said, had been inundated with calls from activists.

However, a group of prospective conference attendees gathered for dinner at another restaurant, Maggiano’s in the Friendship Heights area, and protesters tried to confront them inside.

Midway through the private dinner, more than 30 demonstrators swarmed into the restaurant and tried to reach the second floor area where the dinner was going on.

Restaurant personnel blocked the protesters from reaching the diners,and police later forced them outside. A protest continued on the Wisconsin Avenue sidewalk for about an hour and a half, with posters and chants.

At one point during the turbulence inside the restaurant, a foul-smelling liquid was sprayed on Spencer.

“They’re total scum” he told a reporter later. “They attacked me, they attacked the employees of this restaurant.”

Among protesters’ chants was “No Nazis, No KKK, No Fascist USA.”