“I am unequivocally alarmed by what I saw there,” Mr. Hayden said.
Aides to Representative Kevin McCarthy of California, the Republican leader who hopes to be speaker next year, did not respond to emails or texts seeking comment. Nor did representatives for Mr. Santos, Mr. Mills or Mr. Collins.
Mr. Jeffries, the New York Democrat, said it was highly unlikely Ms. Greene or the three congressmen-elect would not have known the nature of the gathering. In 2018, the Metropolitan Republican Club in Manhattan invited an early leader of the Proud Boys, Gavin McInnes, to speak. The event ended with a melee, a rash of vandalism and three people charged with assault. In 2020, the Young Republican Club held its gala in secret — and in person, without masks — provoking anger over the group’s flouting of Covid rules.
The location of Saturday’s event was announced only 48 hours beforehand, which Mr. Berger said was standard procedure for the group. Mr. Brimelow said going to such lengths before an event “shows that New York City is effectively controlled by communist mobs.”
To Mr. Jeffries, the secrecy of the location was evidence that event organizers understood the controversy of the gathering.
“It’s very unfortunate that some of the incoming Republican House members from New York have chosen to embrace extremists who want to undermine our democracy. They are not getting off to a good start,” Mr. Jeffries said.
Mr. Santos, the only incoming member from New York who was there, is the first openly gay Republican elected without the advantage of incumbency. He made his name in New York politics with his adamant opposition to abortion, which he compared to slavery. But he also was a proponent of the false claims that Mr. Trump had the 2020 election stolen from him, insisting that he, too, had his election stolen in 2020 when he lost by 12 percentage points to then-Representative Tom Suozzi, a Democrat.
Mr. Collins was not Mr. Trump’s pick in the Republican primary for a Georgia district that was redrawn to turn Republican, but he ran as an acolyte of the former president and an election denier. In Florida, Mr. Mills ran largely on his credentials as a decorated combat veteran in a district whose boundaries shifted sharply to become strongly Republican. His Republican primary challenger, Anthony Sabatini, called him a “Republican in Name Only,” but through appearances on One America News Network, he established his conservative bona fides.
