The House Intelligence Committee has issued a subpoena to an associate of Sen. John McCain John Sidney McCainAnalysis: Biden victory, Democratic sweep would bring biggest boost to economy The Memo: Trump's strengths complicate election picture Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE (R-Ariz.) over his connection with the controversial dossier containing unverified allegations about President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE and his ties to Russia, The Hill confirmed on Wednesday.

Committee Chairman Devin Nunes Devin Gerald NunesOvernight Defense: Stopgap spending measure awaits Senate vote | Trump nominates former Nunes aide for intelligence community watchdog | Trump extends ban on racial discrimination training to contractors, military Trump nominates former Nunes aide to serve as intel community inspector general Sunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election MORE (R-Calif.) wants to talk to David Kramer, a former State Department official and current senior director at the nonprofit McCain Institute, about his visit to London in November 2016, a source familiar with the matter confirmed.

The Washington Examiner's Byron York first reported on the subpoena.

While in London, Kramer met with the dossier's author, former British spy Christopher Steele, at McCain's request, to view “the pre-election memoranda on a confidential basis,” according to court filings.

Kramer then flew back to the U.S. and delivered a copy of the memos to McCain, who then handed the documents to the FBI.

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The subpoena for Kramer to appear before House investigators on Jan. 11 comes after he met with the panel earlier this month.

The dossier has long been a key interest of Republicans, who want to find out if its claims were used as the basis for a surveillance warrant on Trump campaign associates.

Democrats, on the other hand, are interested to learn whether the allegations made against the president in the dossier are true.

Certain parts of the dossier have either been confirmed or proven false, while other parts of the memo compilation remain unverified.

The Democratic National Committee and Hillary Clinton Hillary Diane Rodham ClintonFox News poll: Biden ahead of Trump in Nevada, Pennsylvania and Ohio Trump, Biden court Black business owners in final election sprint The power of incumbency: How Trump is using the Oval Office to win reelection MORE's presidential campaign partly funded the dossier, created by the opposition research firm Fusion GPS.

Trump has resoundingly dismissed the memo as "fake."

A spokeswoman for McCain's office did not immediately respond to requests for comment.

— Updated: 4:44 p.m.