Similarly demolished is the Nunes memo’s argument that the F.B.I. falsely implied independent corroboration for Mr. Steele’s claims by citing news reports about his work. The reference to those reports is in a separate section detailing not Mr. Page’s Russian contacts but his public denials — potentially relevant if they included independently falsifiable claims — and a partly redacted footnote suggests the F.B.I. understood those articles to be indirectly derived from Mr. Steele’s work.

An independent line of attack was mounted by the National Review writer Andrew McCarthy, a former prosecutor, who blasted the F.B.I. for relying on Mr. Steele’s “hearsay,” which had not been properly “verified.” While redactions leave the full body of evidence unclear, verification in the FISA context typically refers to compliance with the so-called Woods Procedures implemented in 2001, a process meant to ensure that representations to the court match what’s in the F.B.I.’s case files, not to automatically exclude information provided by a single source. Even in ordinary criminal investigations, current law unambiguously allows hearsay — secondhand information normally inadmissible as evidence in a criminal prosecution — to be used in warrant applications.

Does the application as a whole substantiate the F.B.I.’s belief that “the Russian Government’s efforts are being coordinated with Page and perhaps other individuals associated with Candidate #1’s campaign”? The black bars obscuring whole sections of the published applications make it hard to say, but in the renewal applications — all, like the first, approved by Republican-appointed judges — those redacted sections grow progressively longer, suggesting an accumulation of information, separate from Mr. Steele’s contentious “dossier,” that the F.B.I. regarded as corroborating their initial assessment.

Perhaps, though, that shouldn’t matter: A warrant is supposed to be justified by the evidence at hand before the search, not the evidence the search itself uncovers. And if the parts of the Page application that are now public constituted the whole of the case, that would indeed be thin grounds for a yearlong wiretap on an American.

That, however, would not be a problem of F.B.I. abusing the system; it would be a problem with the system itself. Once we recognize claims about the F.B.I. misleading the court as nonsense, there are only two possibilities: Either the F.B.I. had compelling evidence that Mr. Page was an agent of a foreign power, or four different judges signed off on wiretapping him without such evidence.

It’s obvious why Mr. Trump and his allies would want to deny the first possibility. But the second is equally inconvenient for Mr. Nunes and many of his co-partisans, who have long supported more expansive intelligence surveillance powers and worked furiously to defeat legislative efforts to impose stricter privacy safeguards.

Shortly before releasing his notorious memo, after all, Mr. Nunes was instrumental in reauthorizing a surveillance authority known as Section 702, which permits warrantless interception of Americans’ communications with intelligence targets abroad. And he voted to block proposals that would require judicial approval before F.B.I. agents could sift through the National Security Agency’s vast wiretap database looking for those communications.