It’s been more than a year since a top Republican senator reconstructing the Russia probe demanded answers from the FBI about a post-election briefing for then-President-elect Donald Trump on the unverified dossier of allegations against him – but the bureau has not yet responded.

A congressional source confirmed to Fox News that more than 15 months later, the FBI has still not responded to a May 21, 2018 letter from Wisconsin Sen. Ron Johnson, the chairman of the Senate Homeland Security and Governmental Affairs Committee, asking questions about FBI senior executives, their communications and their actions at the Jan. 6, 2017 Trump Tower briefing on the dossier.

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The FBI declined to comment Wednesday.

The letter specifically asks about the timing of the FBI learning that media outlets had the dossier, FBI prep notes for the briefing and all communications between then-Director of National Intelligence James Clapper and then-FBI Director James Comey. The letter also highlighted an email exchange among senior FBI leadership from then-Deputy Director Andrew McCabe with the subject line “Flood is coming,” indicating that CNN would soon go forward with a “sensitive story." That's believed to be in reference to the dossier.

Comey, CIA Director John Brennan, Clapper and National Security Agency Director Mike Rogers met with Trump at the meeting-- which dealt in part with the Intelligence Community Assessment into Russia’s election interference in the 2016 campaign.

The recently released inspector general's report on Comey indicated how the FBI director and his top deputies went to great lengths to confront Trump at the meeting about the salacious and unverified accusations contained in the dossier, which had been funded by Democrats and drafted by British ex-spy Christopher Steele.

The goal of the briefing, according to witnesses who spoke to the inspector general, was to handle the subject matter sensitively -- to avoid any perception that the one-on-one briefing was an effort to hold information over the president-elect like a "Hoover-esque type of plot."

But, the IG report also found other motives by the FBI.

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Witnesses told the inspector general they discussed the possibility that Trump "might make statements about or provide information of value to the pending Russia interference investigation" – a probe known as "Crossfire Hurricane."

The group, according to the inspector general report, already knew that "several media outlets" had information about the unverified claims in the dossier "and were intending to publish it." The intelligence community directors agreed that the incoming president should be briefed and Clapper decided "the briefing should be done by Comey 'in a small group or one-on-one,'" the report said.

After Comey revealed the dossier claims to Trump, the report said, he observed the president's reactions and quickly documented them for investigative purposes in a record now known as Memo 1.

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Comey later headed to the New York FBI field office to discuss the matter in a secure videoconference with other members of the Crossfire Hurricane team.

Republicans on Capitol Hill have expressed concern over the intentions underlying the meeting.

"The evidence we have is that Comey wasn't going to brief the president just to get him up to speed,” California Rep. Devin Nunes, the ranking member of the House Intelligence Committee, said Tuesday on Fox News' "America's Newsroom." "He was acting as if he was an agent working for the Crossfire Hurricane team, so that is clear evidence that he was involved in this, whereas before, he tried to pretend that he's like a step or two away from what happened."