A senior FBI officer struggled to answer basic questions about antifa, despite characterizing the organization as “the most immediate violent threat” the U.S faces.

At a House Committee on Homeland Security hearing Thursday, Michael Glasheen, operations director of the national security branch of the FBI, said he agreed with President Donald Trump that antifa is one of the greatest national security threats to the country.

“When you look at the data right now, you look at the domestic terrorist threat that we’re facing right now, what I see from my position is that’s the most immediate violent threat that we’re facing on the domestic side,” Glasheen said.

But he was left fumbling when questioned by Rep. Bennie Thompson (D-Miss.), the committee’s ranking member.

“Where in the United States does antifa exist?” Thompson asked.

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

“What does that mean?” responded a baffled Thompson, as he continued to unsuccessfully press for more details on whether antifa exists and how many members they have.

“Well, that’s very fluid,” Glasheen replied. (Watch the exchange below.)

Antifa, which is short for antifascist, is a decentralized movement of mostly progressive activists opposed to fascism and racism.

The organization was designated a “domestic terrorist organization” by Trump last month as the president promised to target left-wing groups following Charlie Kirk’s assassination.

The Anti-Defamation League, which tracks extremists, says that “while some extreme actors who claim to be affiliated with antifa do engage in violence or vandalism at rallies and events, this is not the norm.”