The result is a system that relies almost exclusively on the FBI being scrupulous with its facts. Horowitz’s findings show that the bureau has been systematically unscrupulous.

In the twisted politics of the Trump Era, some of bureau’s defenders might actually view this report as good news: It shows that the investigation of the Trump campaign was not necessarily politically motivated. The bureau made the same kinds of mistakes with suspects who were not connected to the Trump campaign.

That’s hardly reassuring — and the malpractice that the report uncovers is a much larger problem than the FBI and its defenders may wish to admit. So far, the response to Horowitz’s December report has been a series of administrative reforms, such as a requirement that FBI field offices preserve their “Woods files” and a mandate for new FISA training for FBI lawyers and agents. That’s all well and good. But one need not go back to the bad old days of J. Edgar Hoover to see that the bureau has been careless in its monitoring of U.S. citizens.