In the ever-escalating skirmish between U.S. House Democrats and the Trump administration, there’s now a new defendant: Donald McGahn, the former White House counsel and key witness in the special counsel’s investigation of Russia’s interference in the 2016 election.

House Democrats on Wednesday sued McGahn in Washington’s federal trial court to force him to comply with a subpoena seeking testimony about his time leading the White House counsel’s office and interaction with President Trump.