Yesterday, the House of Representatives' Judiciary Committee brought a legal action in federal court (details
here) to compel the Justice Department to turn over all of Robert Mueller's grand jury materials, which may contain valuable evidence of Donald Trump's possible crimes.
The sought materials also include transcripts of interviews with former White House counsel Donald McGahn, who is known to have revealed considerable details about extensive conversations with Trump about actions that could be considered criminal obstruction of justice.
House Judiciary Chairman Jerry Nadler remarked at a press briefing following the filing: "I would say we are in an impeachment investigation, and as to the results of the investigation, it could lead to articles of impeachment or something else."
Because the committee wishes to review the materials with an eye toward possible impeachment, that makes their legal argument considerably stronger and gives Trump almost no valid grounds for defense.
Still, Trump will want to drag this out as long as possible and will have his lawyers paper the court with motions and appeal attempts, hoping he can stall final resolution of the matter until after next year's election, which is fifteen months and one week away.
The danger with that strategy for him is that he can't delay it long enough and the materials are released only a few months -- or weeks -- before the election. What is revealed could effectively torpedo his chances of being reelected.