The memo does state in passing that Mr. Steele’s evidence was an essential part of the application. But we can’t make heads or tails of it without knowing what else was in the affidavit. Whether the memo is revealing a significant error or none at all depends on the big picture that the memo keeps secret. But we have no way to evaluate that, and critics are claiming it’s wrong.

Second, the memo offers scant detail on what the government told the court about Mr. Steele. We get only glimpses. The court knew Mr. Steele had been hired to do his research by a “named U.S. person,” the memo reports. On the other hand, judges were not specifically told about the role of the Democratic National Committee and the Clinton campaign in ultimately funding the investigation.

Without more details, however, it’s hard to know what to make of this. The court might have received a balanced and accurate picture of Mr. Steele’s credibility that did not specifically name the Democratic National Committee or Hillary Clinton. Without knowing all the facts of what the government told the court, we can’t tell if the government did anything wrong.

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?

Finally, the memo questions the government’s evidence based on what we know today rather than what the government knew then. For example, it claims that the application relied on a Yahoo News article since traced to Mr. Steele without explaining the Steele connection.