Did someone say "collusion?"

The Editorial Board of the Wall Street Journal recommends that Robert Mueller resign! They write,

It turns out that Russia has sown distrust in the U.S. political system—aided and abetted by the Democratic Party, and perhaps the FBI. This is an about-face from the dominant media narrative of the last year, and it requires a full investigation.

The Washington Post revealed Tuesday that the Hillary Clinton campaign and Democratic National Committee jointly paid for that infamous “dossier” full of Russian disinformation against Donald Trump. They filtered the payments through a U.S. law firm (Perkins Coie), which hired the opposition-research hit men at Fusion GPS. Fusion, in turn, tapped a former British spook, Christopher Steele, to compile the allegations, which are based largely on anonymous, Kremlin-connected sources.

Strip out the middlemen, and it appears that Democrats paid for Russians to compile wild allegations about a U.S. presidential candidate. Did someone say “collusion”?

This news is all the more explosive because the DNC and Clinton campaign hid their role, even amid the media furor after BuzzFeed published the Steele dossier in January. Reporters are now saying that Clinton campaign officials lied to them about their role in the dossier. Current DNC Chair Tom Perez and former Chair Debbie Wasserman-Schultz deny knowing about the dossier arrangement, but someone must have known.

Perhaps this explains why Congressional Democrats have been keen to protect Fusion from answering dossier questions—disrupting hearings, protesting subpoenas and deriding Republican investigators. Two of Fusion’s cofounders invoked their Fifth Amendment rights last week rather than answer House Intelligence Committee questions, and Fusion filed a federal lawsuit on Friday to block committee subpoenas of its bank records.

The more troubling question is whether the FBI played a role, even if inadvertently, in assisting a Russian disinformation campaign. We know the agency possessed the dossier in 2016, and according to media reports it debated paying Mr. Steele to continue his work in the runup to the election. This occurred while former FBI Director James Comey was ramping up his probe into supposed ties between the Trump campaign and Russians.

Two pertinent questions: Did the dossier trigger the FBI probe of the Trump campaign, and did Mr. Comey or his agents use it as evidence to seek wiretapping approval from the Foreign Intelligence Surveillance Court of Trump campaign aides?

Congressional investigators need to focus on the FBI’s role, and House Speaker Paul Ryan was correct Wednesday to insist that the bureau comply with Congress’s document demands “immediately.” Mr. Sessions has recused himself from the Justice Department’s Russia probe, but he and Deputy AG Rod Rosenstein can still insist on transparency. Mr. Ryan should also reinstall Intelligence Chair Devin Nunes as lead on the Russia investigation, since it appears the Democratic accusations against him were aimed in part at throwing him off the Fusion trail.

All of this also raises questions about Special Counsel Robert Mueller’s investigation. The Fusion news means the FBI’s role in Russia’s election interference must now be investigated—even as the FBI and Justice insist that Mr. Mueller’s probe prevents them from cooperating with Congressional investigators.

Mr. Mueller is a former FBI director, and for years he worked closely with Mr. Comey. It is no slur against Mr. Mueller’s integrity to say that he lacks the critical distance to conduct a credible probe of the bureau he ran for a dozen years. He could best serve the country by resigning to prevent further political turmoil over that conflict of interest.

The American public deserves a full accounting of the scope and nature of Russian meddling in American democracy, and that means following the trail of the Steele dossier as much as it does the meetings of Trump campaign officials.