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(CNN) —  

On Wednesday, Attorney General William Barr told lawmakers that “spying did occur” on President Donald Trump’s 2016 campaign, adding: “I think spying on a political campaign is a big deal.”

Which, if true, it is! Here’s the problem: Barr provided little context or evidence for the “spying” charge. Which is kind of troubling given that he is the top law enforcement official in the country.

Later, he added, “I am not saying that improper surveillance occurred. I am saying that I am concerned about it and I’m looking into it.”

But never mind that right now…

Since Barr provided almost no explanation for “spying” allegation, let’s try to figure out what he’s talking about.

The best guess I can come up with begins with a man named Carter Page. Page, for a time in the Trump campaign, served as a foreign policy adviser to the presidential candidate. Page stepped away from the campaign in September 2016, after articles highlighted his Russian ties. In October 2016, the FBI applied for a warrant to surveil Page under the Foreign Intelligence Surveillance Act (FISA). The warrant was approved. And subsequently renewed three times.

Based on that very simple summation, you could conclude, I suppose, that “spying did occur” on a member of Trump’s presidential campaign. But a fuller picture raises questions about that sort of over-simplification.

According to the FISA warrant for Page, a redacted version of which was released in July 2018, the FBI had been keeping an eye on Page for several years – dating back to at least 2013, when it learned that Russians were trying to recruit American operatives and that Page might be a target. The application also included information from the opposition research document put together by former British spy Christopher Steele, alleging that on a trip to Russia in July 2016, Page met with two Russian officials to discuss lifting US sanctions against the country. (Page denies the meeting.)

“The FBI believes that Page has been collaborating and conspiring with the Russian government,” the application stated, adding that “there is probable cause that such activities involve or are about to involve violations of the criminal statutes of the United States.”

Then there is the matter of how one gets a FISA warrant. In short, it’s not easy. There are 11 judges – all appointed by the Supreme Court chief justice – who sit on something called the Foreign Intelligence Surveillance Court and decide whether or not law enforcement has shown enough evidence to justify the very serious matter of spying on an American citizen. (All of the FISC judges are federal judges, with their own separate docket of cases.) This group hears applications pertinent to FISA.

As April Doss, the one-time senior minority counsel for the Senate Intelligence Committee’s Russia investigation who is now chair of cyber & privacy at the law firm Saul Ewing, told me in 2018:

“All FISA applications go through a lengthy process of approvals within the executive branch as well as in front of the FISC. The details of the process vary according to which section of the FISA legislation is being used to support the application. But the key points for any Title I FISA application are that they go through lengthy internal vetting at the originating agency – in this case at the FBI. That vetting includes a lot of career FBI agents and lawyers and a supervisory special agent before it gets to the level of the FBI director or deputy director for approval. The same thing happens at the Department of Justice, where working-level career attorneys in the National Security Division review the application before it goes to the head of NSD for approval and then to the attorney general or deputy attorney general.”

In short: It’s neither an easy nor a partisan process. Nor is it an illegal one. Spying on an American citizen isn’t something that law enforcement is allowed to do willy-nilly but it is something they are allowed to do if the FISC judge decides they have offered sufficient evidence to prove their need to do so. The fact that Page’s FISA warrant was not only approved but re-authorized three times suggests that a FISC judge found plenty of evidence to suggest the warrant was necessary.

And if you read what Barr said closely, he acknowledges that reality. “I think spying did occur,” Barr said before adding: “The question is whether it was … adequately predicated.”

That is, in fact, the question.

There’s one other thing we have to throw into the mix here: Trump’s own thoughts about reports of surveillance. In a trio of tweets on March 4, 2017, Trump said this:

1. “Terrible! Just found out that Obama had my ‘wires tapped’ in Trump Tower just before the victory. Nothing found. This is McCarthyism!

2. “I’d bet a good lawyer could make a great case out of the fact that President Obama was tapping my phones in October, just prior to Election!”

3. “How low has President Obama gone to tapp my phones during the very sacred election process. This is Nixon/Watergate. Bad (or sick) guy!”

It seems as though he is talking about the Page FISA warrant. (The timing of the warrant’s approval lines up with Trump’s claim.) In addition to the Page FISAs, Trump and his allies have cried foul that the FBI used confidential sources or informants to contact Trump campaign associates in 2016 and ask about their Russian ties.

But what Trump is claiming here simply doesn’t match up with what we know about the FISA process. The President – Obama or anyone else – doesn’t issue or approve FISA warrants. The FISA warrant for Page wasn’t targeted at Trump’s phones in Trump Tower. None of this was focused on the FBI swaying an election against Trump; it was centered on the concern that someone who had worked for the presidential candidate might have been compromised by the Russians.

I suspect – emphasis on the word “suspect” – that Barr knows all of this. But he also knows that by using the word “spying” he is signaling some sort of seemingly nefarious behavior as opposed to the legal and rigorous processes in place that allow law enforcement to surveil an American citizen.

Let’s wait and see what this investigation Barr is conducting into the roots of Page’s surveillance turns up. (The Justice Department’s internal watchdog is also reviewing this and his report is expected this spring, Barr said.) But if past is prologue, the investigation will show that federal law enforcement officials acted entirely within their legal boundaries.