The House Intelligence Committee has issued a subpoena for an associate of Arizona Sen. John McCain’s who revealed last week that he knows the names of the Russian sources used in former British spy Christopher Steele’s infamous dossier.

A congressional source tells The Daily Caller that California Rep. Devin Nunes issued the subpoena on Wednesday for David J. Kramer, a former State Department official.

Kramer refused to divulge the names of Steele’s sources during a Dec. 19 interview with the panel, the source says.

Steele used Russian sources to gather information on the Trump campaign and Donald Trump’s activities in Russia. The ex-spy was working for Fusion GPS, an opposition research firm that was on the payroll of the Clinton campaign and Democratic National Committee.

The Washington Examiner first reported on Nunes’ subpoena for Kramer, which seeks to interview him on Jan. 11.

The identity of Steele’s sources would likely shed light on the veracity of the dossier, which remains largely uncorroborated and has been assailed by President Trump as “crap” and “a hoax.”

Steele relied on Russian government officials and Kremlin insiders for much of the information in the dossier. A former MI6 officer who once worked in Moscow, Steele is reportedly unable to travel back to Russia because of his past spy work. (RELATED: BuzzFeed’s Dossier Source Gets Closer To Being Identified)

Kramer, a former executive at the McCain Institute for Leadership, has been a low-key but central figure in the dossier saga.

He and McCain were first told about the report in Nov. 2016 by Sir Andrew Wood, a former British diplomat and associate of the London-based Steele’s.

On Nov. 28, 2016, Kramer traveled to London to meet with Steele to discuss the dossier. Kramer and Steele arranged for a copy of the dossier to be provided to McCain. After Kramer returned back to the U.S., Steele instructed Fusion GPS to provide a copy of the document to McCain and Kramer.

McCain, who is currently undergoing treatment for brain cancer, provided a copy of Steele’s reports to then-FBI Director James Comey on Dec. 9, 2016.

Steele wrote one additional memo for the dossier four days later. A complete copy was then provided to Kramer and McCain.

BuzzFeed obtained the full 35-page report in late Dec. 2016. The identity of BuzzFeed’s source remains a mystery, though everyone except Kramer who is known to have handled the document has denied providing it to the website.

McCain, Steele and Fusion GPS’s partners have all denied being BuzzFeed’s source.

Attorneys for Aleksej Gubarev, a Russian businessman suing BuzzFeed over the dossier, revealed last week that they recently learned the name of BuzzFeed’s source. That disclosure was made several days after Gubarev’s lawyers deposed Kramer.

The attorneys have said they are unable to identify the source because of a court-imposed gag order in the lawsuit.

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