At some point, the Russia investigation became political. How early was it?

House Intelligence Committee Chairman Devin Nunes appeared on “Fox & Friends” Tuesday, where he provided a potentially explosive hint at what’s driving his demand to see documents related to the Federal Bureau of Investigation’s Trump-Russia probe. “If the campaign was somehow set up,” he told the hosts, “I think that would be a problem.” Or an understatement. Mr. Nunes is still getting stiff-armed by the Justice Department over his subpoena, but this week his efforts did force the stunning admission that the FBI had indeed spied on the Trump campaign. This came in the form of a Thursday New York Times apologia in which government “officials” acknowledged that the bureau had used “at least one” human “informant” to spy on both Carter Page and George Papadopoulos. The Times slipped this mind-bending fact into the middle of an otherwise glowing profile of the noble bureau—and dismissed it as no big deal. But there’s more to be revealed here, and Mr. Nunes’s “set up” comment points in a certain direction. Getting to the conclusion requires thinking more broadly about events beyond the FBI’s actions. Think of the 2016 Trump-Russia narrative as two parallel strands—one politics, one law enforcement. The political side involves the actions of Fusion GPS, the Hillary Clinton campaign and Obama officials—all of whom were focused on destroying Donald Trump. The law-enforcement strand involves the FBI—and what methods and evidence it used in its Trump investigation. At some point these strands intersected—and one crucial question is how early that happened. What may well have kicked off both, however, is a key if overlooked moment detailed in the House Intelligence Committee’s recent Russia report. In “late spring” of 2016, then-FBI Director James Comey briefed White House “National Security Council Principals” that the FBI had counterintelligence concerns about the Trump campaign.

More From The Wall Street Journal (subscription required):