The memo, which was sent to White House staff on Tuesday, comes after Senate Democrats last week asked the White House and law enforcement agencies to keep all materials involving contacts that Trump’s administration, campaign and transition team — or anyone acting on their behalf — have had with Russian government officials or their associates.

The Senate intelligence committee, which is investigating Russia’s role in the 2016 election, has also asked more than a dozen organizations, agencies and individuals to preserve relevant records.

The three administration officials who confirmed that White House staffers were instructed to comply did so on the condition of anonymity because they were not authorized to publicly disclose the memo from White House counsel Don McGahn.

President Donald Trump has been dogged by questions about his advisers’ ties to Russia since the campaign. Federal investigators have been looking into possible contacts between Trump advisers and Russia, while congressional committees are investigating Russia’s role in political hacking during the campaign.

The intelligence community has assessed that Russia’s hacking of Democratic groups and operatives was carried out to help Trump defeat Democrat Hillary Clinton.

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One official said the memo from the counsel’s office instructs White House staff to preserve material from Trump’s time in office, and for those who worked on the campaign, relevant material from the election.

Congressional staffers have said they are not aware of any evidence that materials related to Russia are not being preserved. But Senate Democratic leader Chuck Schumer of New York said last week: “There is real concern that some in the administration may try to cover up its ties to Russia by deleting emails, texts and other records that could shine a light on those connections. These records are likely to be the subject of executive branch as well as congressional investigations and must be preserved.”

Trump has denied having any knowledge that aides were in touch with Russian intelligence agents during the election, as reported by The New York Times. The White House has launched an aggressive effort to discredit the report, including enlisting GOP chairmen of the congressional intelligence committees to push back against it.

The involvement of North Carolina Sen. Richard Burr and California Rep. Devin Nunes has sparked calls — mostly from Democrats — for a special prosecutor to investigate Russia’s role in the election and possible ties to Trump.

The White House has acknowledged that Michael Flynn, Trump’s former national security adviser, misled top officials about the nature of his contacts with Russia’s ambassador to the U.S. Flynn initially told Vice President Mike Pence and other Trump advisers that he did not discuss sanctions with the envoy during the transition, though it was later revealed that he did.

The FBI interviewed Flynn about the contacts days after the inauguration. Trump fired Flynn after the discrepancies in his account were publicly revealed.