Michael Cohen, President Trump’s personal attorney, takes a call near the Loews Regency hotel on Park Avenue on April 13, in New York City. (Yana Paskova/Getty Images)

NBC had what seemed to be a spectacular scoop on Thursday afternoon. For weeks before the FBI raid on his home and office, Michael Cohen’s phones were tapped, the network reported, giving federal investigators access to the content of the phone calls he was making. One of those calls, it was reported, was to someone in the White House.

A few hours later, though, the story changed. There was no wiretap on Cohen’s phones, it turns out, but instead NBC was informed that authorities had obtained a “pen register” on Cohen. On Friday morning, Trump jumped on NBC for getting the story wrong.

The difference between the two types of surveillance is substantial.

David Kris, a former assistant attorney general and founder of the consulting firm Culper Partners, spoke with The Washington Post by phone on Thursday afternoon when NBC’s reporting still indicated that Cohen’s phones had been tapped. When the NBC story was corrected, we spoke again, and he outlined what the new report meant — and how it differed from a wiretap.

“The difference is significant both in terms of what the government has to establish in order to obtain authorization to conduct surveillance whether it be pen register or full-content wiretap, and in terms of what gets collected,” Kris said.

Had the government sought a wiretap of Cohen, Kris explained, it would have needed to fulfill a four-step checklist articulated in the Federal Wiretap Act.

  1. The government would have needed probable cause that Cohen had committed, was committing or was about to commit one of a number of serious crimes, including bribery,  obstruction, terrorism and presidential assassinations.
  2. The government would have had to show probable cause that communication about that crime would be captured by the wiretap.
  3. Reasonable efforts to get the information in traditional ways (informants, subpoenas, etc.) have to have failed — or be believed to be likely to fail. “The idea is that a wiretap is not a first resort in a criminal investigation,” Kris said.
  4. The phone number, line or facility that would be tapped would be in Cohen’s name.

The assessment of whether these criteria are met is made by a special team within the Department of Justice and requires the sign-off of a deputy assistant attorney general.

When the government sought a search warrant for Cohen, it had to fulfill specific guidelines established in the U.S. Attorneys’ Manual to protect conversations between Cohen (an attorney) and his clients (Trump, Republican donor Elliott Broidy and Fox News’ Sean Hannity). In the case of a wiretap, those protections mostly kicked in after the wiretap went up. There are “minimization” procedures meant to keep investigators from being overly intrusive when conducting surveillance on a target, like curtailing their observation of a phone call if it isn’t related to criminal activity. For an attorney, the conversations would generally be reviewed by a “filter team” that’s separate from the core investigative team to protect confidentiality.

After all, a wiretap collects everything: who’s talking, what they’re saying, what numbers they’re calling from. If we use the analogy of your mail, a wiretap would be the equivalent of the government opening and reading your letters.

A pen register — the surveillance being conducted on Cohen — is not that. A pen register is the equivalent of the government looking only at the outside of the envelope, noting who the letter came from and where it’s going and letting it go on its way. (The name comes from a device originally used to record telegraph messages, by using a mechanical pen to register dots and dashes on strips of paper.)

“Pen register — or ‘trap-and-trace’ device — collects the routing, addressing and signaling information, meaning effectively the telephone numbers that are called, not the words that are spoken in a telephone conversation,” Kris explained. “The difference between metadata — or routing, addressing and signaling information — or contents, which is what a full wiretap would get you.”

Since less data is collected through a pen register, the bar for being approved to collect that information is much lower.

What’s needed, Kris said, is “really just a certification by the applicant (who is a [law enforcement officer] or an attorney for the government) that the information likely to be obtained is relevant to an ongoing criminal investigation,” he said. “It’s a mere relevance standard, not like a probable cause standard that applies in the Wiretap Act.”

To give some perspective on what’s revealed in the data collected with a pen register, the federal government until recently collected this data in bulk on every person in the United States. Enacted after 9/11, the goal of law enforcement was to be able to link identify and track terrorism suspects by knowing which numbers were calling which others. The program ended after it was made public by Edward Snowden and President Barack Obama called for it to be wound down.

The point being that at one time the government believed that the metadata collected was sufficiently nonintrusive that it wasn’t a violation of Fourth Amendment protections against improper searches. (Courts, mind you, didn’t entirely agree.)

That’s what the government was collecting on Cohen and how investigators knew there was a call between a Cohen phone and the White House. But that’s just about all they learned.