Did Barack Obama's FBI spy on the Trump campaign by placing a long-trusted source in position to develop contacts with Donald Trump's political advisers? Or did the FBI get information from a well-regarded patriot with concerns over potential damage from hostile foreign intelligence operations?

We're about to find out.

At the heart of these questions lie the credibility and standing of the special counsel probe into Russian meddling and alleged Trump collusion during the 2016 election cycle. And the public's (and president's) demand for answers will test the credibility of Attorney General Jeff Sessions, Deputy Attorney General Rod Rosenstein, and FBI Director Christopher Wray.

The Russia probe began as an FBI counterintelligence investigation more than two years ago, when the bureau got tipped that Trump campaign advisers were discussing their contacts with Russia. How they got tipped and how they reacted, however, is a narrative that keeps changing. Initially, the FBI was reluctant to discuss it, but after the exposure of the Christopher Steele dossier, anonymous "officials" leaked to The New York Times instead that former Australian foreign minister Alexander Downer had contacted the FBI well before the dossier's creation. Downer, now an ambassador to the U.K., had heard Trump foreign-policy adviser George Papadopoulos discussing in May 2016 how Russians had "thousands" of Hillary Clinton's emails. Downer shrugged it off at the time, but after emails began emerging from the DNC hack, Australian officials passed that information along to the FBI. Thus, the Times reported last December, was the birth of the Russian-interference operation.

Until recently, that narrative didn't include an informant that may or may not have been inside the Trump campaign. (There is some dispute over whether such an informant merely met with a few campaign officials or, as the president seems to believe, was "embedded" in the campaign.) House Intelligence Committee chair Devin Nunes (R-Calif.) suspected that the DOJ had held back key information about the origin story, even though his committee had subpoenaed both the DOJ and FBI. As part of the effort to get more information, Nunes threatened to impeach Rosenstein to force the DOJ into compliance with Congress' constitutional oversight role.

Rosenstein made more information available, but not long afterward, the narrative began to shift. The Wall Street Journal's Kimberly Strassel began connecting the dots and reported that the FBI had placed a "top secret intelligence source" in or around the Trump campaign, a source that had a long record of working with both the FBI and the CIA. "This would amount to spying," Strassel wrote, noting that it called into question precisely what started the counterintelligence operation. "When precisely was this human source operating? Because if it was prior to that infamous Papadopoulos tip, then … it would mean the bureau was spying on the Trump campaign."

Anonymous officials pushed back on this contention almost immediately. CNN's sources insisted that the source came to the FBI rather than the other way around, but also included a curious nugget: The informant had not been "planted" by the FBI, but "has been a source for the FBI and CIA for years." Left unanswered: How did a top-secret intel source come into contact with a presidential campaign in the first place, and why would either of those agencies risk his exposure?

A report from The Washington Post on Friday raised even more questions. Rather than being a passive witness/whistleblower, the "secret informant for the FBI" appeared to be actively contacting Trump campaign advisers looking for evidence. The "retired professor … took the opportunity to strike up a conversation with Carter Page," the man whom the FBI would later surveil with a warrant from the FISA court. The informant later contacted campaign co-chair Sam Clovis to offer his services as an adviser, and also offered to fund a research effort by Papadopoulos.

That sounds like something different than mere whistleblowing, especially when conducted by an experienced intelligence "source." It suggests that the informant was either freelancing as a curious sort of "spy lite," or had been tasked to do so more officially by the agency with which he was working. Either way, it calls into question what motivations went into this and whether strong prohibitions against spying on domestic politics may have been violated. These concerns ought to remain whether the informant was "embedded" in the campaign or just approaching its members from outside.

The DOJ's inspector general had already begun probing the investigation itself for any irregularities. This sequence of events would eventually have fallen within IG Michael Horowitz' purview, regardless of whether he received specific direction on the "plant." Rather than allow that to unfold organically, however, President Trump threw gasoline on the fire this weekend after the Post's revelations by demanding (on Twitter, naturally) that the DOJ open a probe into the use of this informant.

That put Rosenstein in the difficult position of having to respond publicly to a demand that likely would have already been met. He announced — ahead of a formal demand — that the IG would expand the scope of his current probe to include concerns over any "irregularities" involving the informant. Critics from all sides attacked the move; Trump opponents claiming that the president had abused his power by forcing the DOJ to investigate its investigation, while Trump supporters accused Rosenstein of dodging the issue by assigning it to an office without subpoena power.

Former DOJ prosecutor Andrew McCarthy argues at National Review that Rosenstein got it right, at least as a start. Potential misconduct gets addressed by either the IG or the Office of Professional Responsibility, neither of which has subpoena power, but that doesn't have to be the only effort. Along with the expansion of the IG probe, McCarthy advises that another probe of the FISA issues being conducted by U.S. Attorney John Huber be expanded to include these allegations too. "It is virtually certain that the new allegations of political spying," he concludes, "which arise out of the same counterintelligence probe against the Trump campaign that resulted in the controversial FISA surveillance, would also fall within Huber's investigative jurisdiction."

And should. Perhaps nothing untoward took place in this FBI investigation, and the steps taken can be shown to be both prudent and responsible. However, the use of long-term intelligence sources to actively engage political campaigns for the purpose of investigating them raises all sorts of dangers of politicization of both law enforcement and intelligence. That kind of activity should only be undertaken if it can survive the highest levels of scrutiny afterward — and that's precisely why it requires that level of scrutiny now. Otherwise, these kinds of activities will become a permanent fixture in our electoral processes, setting up irresistible incentives for those in power who wish to remain in power.