WASHINGTON — A former White House lawyer defied a congressional subpoena Tuesday, setting the Trump administration on course for another collision with the Democratic-led House over its pursuit of documents related to the Russia investigation.

Don McGahn’s refusal to provide the documents to the House Judiciary Committee came at the instruction of the White House, which suggested they could be subject to executive privilege. Such a claim can shield some presidential material from disclosure.

President Donald Trump has defied requests from House Democrats since the release of special counsel Robert Mueller’s report last month. Republicans have largely united behind the president, with Senate Majority Leader Mitch McConnell on Tuesday declaring “case closed”  on Mueller’s Russia probe and potential obstruction by Trump. McConnell said Democrats are “ grieving”  the result.

Mueller said he could not establish a criminal conspiracy between the Trump campaign and Russia, but did not reach a conclusion on whether Trump obstructed justice. Mueller didn’t charge Trump but wrote that he couldn’t exonerate him, either.

Democrats say the case is anything but closed and are conducting their own review of Mueller’s investigation of Russian election interference . The Judiciary panel wants to speak to McGahn and review certain documents, in part because he was a vital witness for Mueller, recounting the president’s outrage over the investigation and his efforts to curtail it.

White House counsel Pat Cipollone said McGahn does not have any “legal right”  to the materials because they are controlled by the White House. Cipollone did not invoke executive privilege in a letter to House Judiciary Chairman Jerrold Nadler, D-N.Y., but strongly signaled the option is on the table. He said the records Democrats are seeking “ remain legally protected from disclosure under longstanding constitutional principles.”

Executive privilege is the president’s power to keep information from the courts , Congress and the public to protect the confidentiality of the Oval Office decision-making process. There is no reference to executive privilege in the Constitution, but the Supreme Court has held that it derives from the president’s ability to carry out the duties the commander in chief holds under the Constitution.

Besides documents, the House Judiciary Committee’s subpoena asked McGahn to testify later this month. Trump has signaled he will try to block McGahn from appearing. McGahn’s lawyer said that he will “ maintain the status quo”  and wait for the White House and the committee to reach an agreement.

“As you will appreciate, Mr. McGahn, as a former assistant to the president and the most senior attorney for the president in his official capacity, continues to owe certain duties and obligations to the President which he is not free to disregard,”  wrote attorney William Burck.

The struggle over McGahn’s testimony is playing out against the backdrop of a larger debate on Capitol Hill about what action — if any — to take following the conclusion of Mueller’s investigation.

McConnell, in his most significant public comments yet on the investigation, opened the Senate on Tuesday with a speech discussing how Mueller’s “exhaustive”  probe is now complete.

“It’s finally over,”  the Kentucky Republican said. He called Mueller’s findings “ bad news for the outrage industrial complex but good news for the rest of the country.”

The speech drew swift rebuttals from Democrats. House Speaker Nancy Pelosi and Senate Democratic leader Chuck Schumer issued a joint statement calling it “ a stunning act of political cynicism and a brazen violation of the oath we all take.”

After McConnell’s speech, Massachusetts Sen. Elizabeth Warren, a Democratic presidential candidate, made her own trip to the Senate floor to say the House should begin impeachment proceedings — a step that Pelosi has so far resisted. Yet Pelosi also said Trump seems to be “ making the case”  for his impeachment by brazenly obstructing investigations.