On Oct. 28, 2013, President Barack Obama and James Comey participate in the installation ceremony for Mr. Comey as FBI director at the bureau’s Washington headquarters. PHOTO: CHARLES DHARAPAK/ASSOCIATED PRESS

The list of Obama-era DOJ and administration officials connected to the Russia collusion investigation into the Trump campaign — an investigation that concluded with an exoneration of the campaign last week with the release of the Mueller report — is impressive.

Those suspected of shopping or leaking the dossier created by Fusion GPS and former British agent Christopher Steele —  paid for their work by Hillary Clinton’s law firm Perkins Coie — include former FBI Director James Comey, former Director of National Intelligence James Clapper, and former Director of the Central Intelligence Agency John Brennan. Not to mention the numerous agents and officials within the FBI and DOJ who ferried the information and worked to obtain FISA warrants to spy on Trump associates.

Now that the Mueller report has concluded there was no collusion, James Freeman assistant editor of  The Wall Street Journal’s editorial page, is calling for former President Barack Obama to explain what he knew about the investigation and when he knew it.

“The former President now owes the country an explanation for the historic abuse of government surveillance powers,” Freeman writes.

The Mueller report confirms that the Obama administration, without evidence, turned the surveillance powers of the federal government against the presidential campaign of the party out of power. This historic abuse of executive authority was either approved by President Barack Obama or it was not. It’s time for Mr. Obama, who oddly receives few mentions in stories about his government’s spying on associates of the 2016 Trump campaign, to say what he knew and did not know about the targeting of his party’s opponents.

If he was briefed, for example, on plans by the Justice Department to seek wiretaps on Trump campaign associates, it’s hard to believe Mr. Obama would not have been highly interested in the matter. Going all the way back to his campaign for a U.S. Senate seat in Illinois, Mr. Obama had aggressively advocated for preventing federal abuse of surveillance powers.

Columnist and lawyer Andrew McCarthy poses a similar question to Mueller himself in a piece at Fox News:

Now that Special Counsel Robert Mueller has concluded that there was no criminal collusion, the question arises: When during their exhaustive 22-month investigation did prosecutors realize they had no case?

I put it at no later than the end of 2017. I suspect it was in the early autumn.

By the time Mueller was appointed on May 17, 2017, the FBI had been trying unsuccessfully for nearly a year to corroborate the dossier’s allegations. Top bureau officials have conceded to congressional investigators that they were never able to do so – notwithstanding that, by the time of Mueller’s appointment, the Justice Department and FBI had relied on the dossier three times, in what they labeled “VERIFIED” applications, to obtain warrants from the Foreign Intelligence Surveillance Court.

And make no mistake about what this means. In each and every application, after describing the hacking operations carried out by Russian operatives, the Justice Department asserted:

The FBI believes that the Russian Government’s efforts to influence the 2016 U.S. presidential election were being coordinated with Page and perhaps other individuals associated with [Donald Trump’s] campaign.

Yes, the Justice Department continued to make that allegation to the secret federal court for months after Trump was sworn in as president.

In short: why did Obama allow the investigation within his agencies if they had no proof of collusion, and why did Mueller sit on his knowledge of a lack of collusion until last week?