House lawmakers on Wednesday requested that former National Security Adviser John Bolton testify in the impeachment inquiry into President Donald Trump.

Bolton was ousted from the White House last month after months of strong disagreements with Trump and other administration officials on foreign policy issues. Bolton’s testimony is expected to cement him as a key witness in the impeachment inquiry, which has already produced uncovered damning revelations about the president’s effort to enlist Ukraine to investigate his political opponents.

Bolton’s aides have testified that the former national security adviser was furious when he learned about Trump’s attempts to pressure Ukraine’s government to probe prominent Democrats like former Vice President Joe BidenOne aide, Fiona Hill, told House investigators earlier this month that Bolton called Trump’s personal lawyer Rudy Giuliani — who was leading the effort to press Ukraine — “a hand grenade who’s going to blow everybody up.”

Hill also said in her testimony that Bolton told her he wanted no involvement in any dealings with Ukraine that White House Chief of Staff Mick Mulvaney and Ambassador to the European Union Gordon Sondland were partaking in. Mulvaney had reportedly been tasked with pulling military aid from Ukraine until the country’s government gave the Trump administration damaging information on Biden and his son. Trump and his administration had also pushed for a meeting between the president and his Ukrainian counterpart at the White House as part of their quid pro quo.

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“I am not part of whatever drug deal Sondland and Mulvaney are cooking up,” Bolton reportedly told Hill to say at her deposition.

It remains unknown whether or not Bolton will actually testify before House investigators, however, as he has not been formally subpoenaed. Bolton’s lawyer said his client was “not willing to appear voluntarily.”

Bolton is scheduled to appear before lawmakers on Nov. 7, just three days after National Security Council lawyers Michael Ellis and John Eisenberg are set to testify.