WASHINGTON — House Speaker Nancy Pelosi sought Monday to deprive President Trump of a legal and political argument against the Democrats’ impeachment inquiry, announcing she would hold a vote in the full House this Thursday that “affirms the ongoing, existing investigation.”

“We are taking this step to eliminate any doubt as to whether the Trump Administration may withhold documents, prevent witness testimony, disregard duly authorized subpoenas, or continue obstructing the House of Representatives,” Pelosi said in a written statement. “Nobody is above the law.”

Pelosi said the Trump White House has made a “baseless claim that the House of Representatives’ impeachment inquiry ‘lacks the necessary authorization for a valid impeachment proceeding.’”

That was a quote from a letter that Trump’s White House counsel, Pat Cipollone, sent to Congress on Oct. 8 rejecting cooperation with the impeachment inquiry.

“They argue that, because the House has not taken a vote, they may simply pretend the impeachment inquiry does not exist,” Pelosi said. “Of course, this argument has no merit.”

Much of the reason that the House held votes in 1974 and 1998 to begin impeachment proceedings against President Richard Nixon and President Bill Clinton was because such a vote was needed to do the investigative work of issuing subpoenas and holding depositions. Over the last decade or two, the rules of Congress have changed so that a full House vote is no longer necessary.