The #Spygate conspiracy theory started, as so many things do these days, with a tweet from President Donald Trump:

“Apparently the DOJ put a Spy in the Trump Campaign. This has never been done before and by any means necessary, they are out to frame Donald Trump for crimes he didn’t commit.” David Asman @LouDobbs @GreggJarrett Really bad stuff! — Donald J. Trump (@realDonaldTrump) May 18, 2018

Initial reports in the New York Times and the Washington Post described the “spy” as a U.S. professor living in the United Kingdom who had met with Trump campaign aides on orders from the FBI in the summer of 2016.

The reports provided enough detail about the informant — or, to use the FBI’s preferred term, “confidential human source” — that some quick Googling allowed journalists, including The Intercept’s Glenn Greenwald, to identify him as Stefan Halper, a retired University of Cambridge professor who was involved in an effort in 1980 to help Ronald Reagan spy on President Jimmy Carter’s re-election campaign. Halper, who worked for three previous Republican administrations and reportedly provided information to the CIA, has raked in more than $1 million in U.S. Defense Department contracts in just the last five years.

As with many of Trump’s conspiracy theories, #Spygate contains a kernel of truth. The FBI has an informant problem. With more than 15,000 informants today — 10 times as many as J. Edgar Hoover had during his era of intrusive surveillance operations — the FBI has loose regulations on how agents can recruit and run informants, who turn to the bureau to make a lot of money or avoid deportation, among other reasons. A decade ago, the FBI spied on Muslims throughout southern California with no reason for suspicion other than their religion. Informants regularly commit crimes, including while investigating accused terrorists. The bureau’s roster of informants has included terrorists such as Al Qaeda operative Najibullah Zazi, murderous criminals such as mobster Whitey Bulger, and even traitors to their causes like Ernest Withers, who reported to the FBI as he was building a reputation as the photographer of record for the civil rights movement.

With #Spygate, Trump has wrapped his conspiracy theory — that the FBI inserted an informant into his presidential campaign — around a fundamental truth about the FBI’s misuse of informants and then, further burnishing his reputation as a modern-day P.T. Barnum, sent it into the world with plenty of rhetorical flourish.

“The FBI could be the world’s most successful PR agency. They excel at making themselves look good. You realize that early on as an agent,” said Jeffrey A. Danik, a retired supervisory FBI agent. “The problem with the FBI today is that they’ve come up against one of the truly great marketing geniuses in Donald Trump. Their normal PR and spin is getting hammered by the PR spin master. He knows exactly which word will sell. ‘Spy’ is perfect.”

The FBI’s defense has been to disassociate itself from the term “spy,” even though that is exactly what FBI informants do whether they are working criminal or national security investigations. Instead, the bureau’s surrogates have been peddling the fiction that its informants have not been a constant source of scandal.

Former FBI Director James Comey commented this month that FBI informants are “tightly regulated,” a demonstrably false statement. (Read the FBI’s “Confidential Human Source Policy Guide” for yourself.)

Asha Rangappa, a former FBI agent who wears a T-shirt bearing the red, white, and blue words #ComeyIsMyHomey when she’s not defending her former employer on CNN, argued in a Washington Post op-ed that informants deployed in national security investigations are somehow different from the ones used in criminal inquiries. She described Halper as an “intelligence source,” rather than an informant — a convenient but meaningless distinction, because FBI informants aren’t siloed. An informant could be working a criminal investigation one day and a national security inquiry the next, or a criminal investigation could become a national security concern, and vice versa. That’s a primary reason that Special Counsel Robert Mueller, as FBI director, argued against a post-9/11 proposal to split the bureau into two agencies, one for intelligence and another for criminal investigations.

But while the FBI’s defenders seek to distance the bureau from the word “spy,” giving #Spygate even more momentum, they’re not talking about one clear sign that Trump’s claim of politically motivated spying is indeed a conspiracy theory.

Halper, the FBI’s informant, was a U.S. citizen living in London. Because he was overseas, he would have been considered, in the FBI’s parlance, an “ET CHS” — extraterritorial confidential human source — which means that the FBI would have been required to follow significantly more onerous rules than if he were spying in the United States.

Under the FBI’s informant guidelines, agents are permitted, through time-limited investigations known as “assessments,” to use informants to spy on people in the U.S. without having reason to believe they are committing crimes or posing national security concerns. Assessments have so few safeguards that their use in politically motivated spying is not implausible, though there’s no known case of this to date.

But assessments aren’t available to the FBI when working outside the U.S. To deploy an overseas informant, the FBI’s informant guidelines require agents to have a full investigation open. Such an investigation requires an “articulable factual basis” — in other words, evidence that a national security concern might exist or criminal activity may be occurring. An unsubstantiated tip, while enough to support the opening of an assessment, would not be enough to initiate a full investigation that could be used to task an informant working internationally.

Halper reportedly met with Trump campaign foreign policy adviser Carter Page in July 2016, prior to the FBI’s opening of its Trump-Russia investigation, code-named Crossfire Hurricane. This by itself is not scandalous, since the FBI was at the time investigating Russia’s alleged efforts to recruit Page as a spy of their own. In 2013, the bureau had obtained recordings of Russian agents discussing their approaches to Page. Those recordings, coupled with Page’s meeting with Russian officials in Moscow in July 2016, likely would have been enough to open a full investigation, making Halper’s activity in London perfectly justifiable under FBI rules.

Halper’s later known activity — meeting with Trump campaign aides Sam Clovis in August 2016 and George Papadopoulos in September 2016 — happened after the opening of Crossfire Hurricane, which again would have required an “articulable factual basis,” making baseless and politically motivated spying of the kind that Trump has alleged highly unlikely.

What’s more, because the FBI ran Halper as an overseas informant, any spying would have been documented in Delta, the FBI’s program for managing informants, creating a long paper trail about why the FBI chose to use Halper and what agents tasked him with doing. This is likely among the classified information Trump demanded that FBI Director Christopher Wray and Deputy Attorney General Rod Rosenstein provide to select senators and congressional representatives.

After reviewing the FBI’s materials, Republican U.S. Rep. Trey Gowdy this week dismissed #Spygate on Fox News as the conspiracy theory that it is: