Rep. Devin Nunes is trying to determine how far and wide the unverified Russia-Trump dossier spread inside the U.S. government, especially among senior leaders in President Obama’s administration during the 2016 election.

The chairman of the House Permanent Select Committee on Intelligence released a letter Tuesday that is being sent to as many as two dozen senior leaders in the Trump and Obama administrations.

The California Republican is asking 10 questions to gauge who received the dossier information and what they did with it.

The dossier, funded by Hillary Clinton campaign and the Democratic Party and written by British ex-spy Christopher Steele, was circulated by paymaster Fusion GPS during the 2016 campaign.

Mr. Steele, relying on Kremlin sources, made a series of felony charges plus several salacious claims against Mr. Trump and his aides. None to date have been confirmed publicly.

The letter’s recipients are redacted. But it is assumed they are going to be such leading Obama administrations officials as CIA Director John Brennan and Director of National Intelligence James Clapper.

One question asks, “When and how did you first become aware of any of the information contained in the Steele dossier?”

Another is “Was President Obama briefed on any information contained in the dossier prior to Jan. 5, 2017.”

Then-FBI Director James B. Comey personally briefed Mr. Trump on the dossier on Jan. 6.

Mr. Nunes has been conducting a parallel investigation in the Trump-Russia collusion probe.

He has revealed that the Democrats paid for the dossier and that the FBI used it to obtain a year’s worth of wiretap warrants on Trump volunteer Carter Page.

Mr. Nunes also discovered through persistent document requests to the FBI that the bureau authorized payments to Mr. Steele to continue investigating Mr. Trump as president-elect and possibly as president. But it fired him after he went to the press in October 2016 to disclose his FBI collaboration.

And Mr. Nunes discovered that Mr. Steele lied to the FBI when he denied being the source for a Yahoo News story. Based on his denial, the FBI used the story as corroboration for the dossier in wiretap warrant applications — four times over nearly a year. Mr. Steele admitted in a London court filing that he was indeed the Yahoo source.

Senate Judiciary Committee Chuck Grassley, Iowa Republican, has been doing his own dossier investigation.

Taking the probe one step further, he and Sen. Lindsey Graham, South Carolina Republican, sent a referral asking the Justice Department to investigate Mr. Steele for lying to the FBI about the Yahoo News story.

The FBI agreed to un-redact much of the referral. It showed that a Obama State Department official served as a middleman during the election in hooking up two Clinton political operatives with Mr. Steele.