In light of the information coming from Australia, this conduct was actually a relatively unintrusive way to start an investigation.

Contrast that with the investigation of Mayor Tony Mack of Trenton. In 2010, an F.B.I. informant met with one of Mr. Mack’s supporters and offered cash in exchange for Mr. Mack’s help in obtaining property to build a parking garage. Mr. Mack was eventually convicted of six federal charges. Similarly, in 2014, the F.B.I. used the chief of staff to New York State Senator George D. Maziarz to gather information on him. The F.B.I. used an informant to take down former congressman William Jefferson and one to prosecute the Hoboken mayor Peter Camarano. And in the investigation into the congressional campaign of Connecticut State Representative Chris Donovan, federal agents employed an informant and an undercover agent and staked out a political convention.

In its investigation into Russia’s potential connection to the Trump campaign, the F.B.I. obtained warrants to surveil the communications of Mr. Page and the campaign chairman Paul Manafort. The F.B.I. sought the wiretaps from the Foreign Intelligence Surveillance Court, rather than a district court, because the applications contained sensitive foreign intelligence information. Ordinarily, to get to the FISA Court, the agents prepare an application and send it for review to the supervisor, the chief division counsel, the special agent in charge and then a unit supervisor at F.B.I. headquarters. It then goes to the National Security Division at the Justice Department for a verification procedure before arriving at a FISA judge who does a review of the material to see whether surveillance is warranted. In Mr. Page’s case, most of the judges reviewing his application were actually Republican appointees.

The process of obtaining a FISA warrant to wiretap is slightly different from the process used in a district court, but the authorized surveillance technique — in other words, the “spying” — is the same. Again, this is a common investigatory method when the government can show probable cause to a court. The F.B.I. wiretapped Representative Rick Renzi in an extortion and racketeering investigation. Governor Rod Blagojevich of Illinois was wiretapped trying to sell President Barack Obama’s former Senate seat. Associates of Mayor Joe Ganim of Bridgeport, Conn., were also secretly recorded in a wide-ranging corruption investigation.

The attorney general’s response to Senator Hawley had the unique quality of being simultaneously true and misleading. They were both playing a linguistic sleight of hand. We’ve had only 45 presidents and 58 presidential elections in history. It should be no surprise — and should in fact be a relief — that federal investigators had never needed to use such techniques to investigate a presidential campaign.

But make no mistake, in the broad context of high-profile public corruption investigations, the methods used against Mr. Trump’s associates are by no means an anomaly.

What is anomalous is the effort by some Republicans to undermine legitimate counterintelligence concerns. After Mr. Barr’s testimony, Senator Hawley tweeted that “the F.B.I. spied on @realDonaldTrump and launched multiyear investigations” because “unelected progressive elites in our government have nothing but contempt for” Trump voters.