There could have been more than one FBI informant snooping on the Trump campaign, House Intelligence Committee Chairman Devin Nunes said on Sunday, but we do not know because the Justice Department has stonewalled congressional requests for documents outlining the impetus for the investigation.

Multiple reports have identified Stefan Halper, 73, a Cambridge professor with ties to American and British intelligence, as the FBI informant who snooped on the Trump campaign over the summer.

Mr. Nunes said he may not be the only one.

“We asked for specific documents that we have still not received from the Department of Justice,” Mr. Nunes said on Fox News’ “Sunday Morning Futures.” “So they continue to leak out things about this informant, and we don’t know if there’s one informant or more informants because there’s so much out there now. It’s really getting tough to follow, and all we’re asking for is give us the documentation that you used to start this investigation.”

The New York Times reported on Friday that an “American academic who teaches in Britain” met with Trump campaign advisers Carter Page and George Papadopoulos in the summer of 2016.