A top FBI official toed the White House line about antifa as a major domestic terror threat at a House hearing on Thursday — but he struggled to answer questions about the leaderless movement.

Pressed repeatedly by a top Democrat on the House Homeland Security Committee about antifa’s size and location, the operations director of the FBI’s national security division didn’t have answers.

At one point, the FBI’s Michael Glasheen fumbled with his hands as he tried to find an answer for the question from Rep. Bennie Thompson, D-Miss.

“Well, the investigations are active,” Glasheen said.

Glasheen’s comments came three months after President Donald Trump proclaimed that antifa is a “major terror organization,” even though it the broad political movement does not have a hierarchy or leadership.

Trump followed his designation with a presidential memo on September 25 directing the FBI-led Joint Terrorism Task Forces to investigate and prosecute antifascists and other adherents of “anti-Americanism.”

The formless nature of the antifascist movement, however, appears to have flummoxed the FBI as it attempts to carry out Trump’s orders.

Glasheen called antifa “our primary concern right now” and called it “the most immediate, violent threat” from domestic terrorists. That led Thompson to ask him where antifa is located and how many members it has.

“We are building out the infrastructure right now,” Glasheen said.

“So what does that mean?” Thompson shot back. “I’m just — we’re trying to get the information. You said antifa is a terrorist organization. Tell us, as a committee, how did you come to that? Where do they exist? How many members do they have in the United States as of right now?”

“Well, that’s very fluid,” Glasheen said. “It’s ongoing for us to understand that. The same, no different than Al Qaeda or ISIS.”

Glasheen visibly struggled to answer the question before saying that the FBI’s investigations were “active.”