A follow-up review suggested that the F.B.I.’s botching of FISA applications has been systematic rather than focused on Mr. Page in particular. The inspector general looked at the F.B.I.’s preparation to request 29 unrelated national-security wiretaps and uncovered problems with all 29 of them. In response, the F.B.I. tightened its procedures and the FISA court and Congress increased their oversight.

Still, a top official cautioned against interpreting the decline in the number of suspects that the F.B.I. sought court permission to wiretap in national security investigations as “seemingly reflecting the events of the day.” The figure includes American targets anywhere in the world, as well as noncitizens on American soil like foreign diplomats.

The official, Benjamin T. Huebner, the chief civil liberties, privacy, and transparency officer at the Office of the Director of National Intelligence, suggested to reporters that fluctuations could be driven by a variety of factors, such as a “change in the terrorism threat” and world events.

He also noted that the number of FISA orders — as opposed to people targeted by those orders — has been on a steadier downward trend. (The F.B.I. can bundle requests to target more than one suspect into the same application for an order.)

A senior Justice Department official, speaking on condition of anonymity in the same briefing with reporters, echoed his points and said she had no information that the number of targets declined based on any “fear of using the FISA tool.”

Both also noted that the government’s use of its traditional FISA powers to obtain a court’s permission to wiretap particular targets has been on an overall downward trend since 2007 and 2008, when Congress adjusted the law to permit warrantless wiretapping of foreigners abroad. Before that, investigators also had to get individual warrants to collect emails from American companies, like Google and Yahoo, in the accounts of noncitizens abroad.

The number of foreign targets of such warrantless surveillance — sometimes known as Section 702, after the portion of the FISA Amendments Act of 2008 that authorizes it — has been on a continuous upward trend since at least 2013 and did not divert from it last year, when there were 204,968 such targets. In 2018, there had been 164,770 such targets.