Tim Morrison, a senior director for Russian affairs on the National Security Council, said through his attorney Friday he would testify if subpoenaed by House impeachment investigators, becoming the first current White House officials to appear before the panel.

Investigators have scheduled a closed-door deposition for next Thursday as the early phase of the impeachment inquiry winds down. Public hearings could begin as early as mid-November.

President Trump has refused to cooperate with the investigation and blocked several administration figures from being deposed. The latest refusal came from Russell Vought, acting director of the Office of Management and Budget who had been scheduled to testify Friday.

The Hill reported attorney Barbara Van Gelder confirmed Morrison would appear but declined to preview what he has to say.

Democrats say they believe he was among those on hand for Trump’s July 25 phone call with Ukraine President Volodymyr Zelensky during which he asked his Ukrainian counterpart for a “favor” -- an investigation of former Vice President Joe Biden and a debunked conspiracy theory involving Ukrainian interference in the 2016 presidential election.

The phone call is at the heart of the impeachment probe.

The Hill said Morrison also likely could corroborate testimony from Ukraine envoy Bill Taylor, who testified Morrison made him aware of several conversations in which the administration was seeking a quid pro quo before it would free $391 million in military aid authorized by Congress to fight Russia-backed separatists in Ukraine’s eastern provinces.

Several career officials have defied White House instructions and testified before investigators under subpoena, painting a damning picture of administration actions.

Former Sen. John Kerry, D-Mass., told CNN he thinks the evidence against Trump is “more powerful” than that against Richard Nixon, who resigned as president shortly before a House vote on impeachment.

The White House has yet to put together a team to handle impeachment developments. CNN reported former Treasury Department spokesman Tony Sayegh is being eyed to lead impeachment messaging efforts. Trump is said to be opposed to setting up a war room to deal with the situation and has yet to sign off on Sayegh’s hiring.

In the meantime, the Justice Department has opened a criminal investigation into what touched off the investigation into possible collusion between the 2016 Trump campaign and Russia. An investigation by former Special Counsel Robert Mueller found that while there was no collusion, Russia interfered in the campaign on Trump’s behalf. It was not immediately clear what crime was being investigated by Justice.

Trump has made clear he sees the formerly independent Justice Department as a tool to use against his political opponents. He has called the FBI investigation into his campaign “treasonous.”