Third, the memo ignores the fact that judges usually expect informants to be biased without being told of it. Judges routinely uphold warrants in criminal cases that fail to disclose bias in informants far worse than Mr. Steele’s. An informant might be the target’s wife, who the government fails to point out is engaged in a bitter divorce battle with him. An informant might be a known criminal facing fresh charges, who the affidavit fails to disclose was promised a break if he shares information about others.

Judges expect this. As a result, courts say, it’s not necessarily a problem to omit it from the warrant affidavit. As one appellate court has written, only a “very naïve” judge would expect a source to “drop in off the street with such detailed evidence and not have an ulterior motive.” And who is more likely to lie: Criminals promised leniency or a former British intelligence agent hired for his expertise?