It is crucial to understand that the general oversight power and the specific impeachment-investigation power are not mutually exclusive. In other words, if Congress is concerned that a president is acting contrary to law or misbehaving in his direction of agencies of the executive branch, that is a proper subject of its oversight authority. Inquiring into the conduct of the executive branch, including its constitutional head, is the purpose of the oversight power. The fact that the president’s behavior in a particular matter might become grounds for impeachment doesn’t exempt that matter from ordinary oversight.
With this constitutional background in mind, consider the sequence of events that led to Trump’s impeachment.
On August 28, 2019, Politico reported that aid to Ukraine previously authorized by Congress was being withheld by the Trump administration. Within a week, The Washington Post reported that the hold might have been placed to induce Ukraine to investigate Joe Biden and his son Hunter. This was obviously a matter of legitimate legislative concern because it related both to the proper expenditure of particular congressionally appropriated funds and to more general issues of the conduct of American foreign policy and election integrity. Not to mention it also implicated the president’s own conduct.
Maya Wiley: This is a trial of the Constitution itself
Accordingly, on September 9, three standing House committees—Foreign Affairs, Intelligence, and Oversight—announced investigations into the blocked aid. Two days later, on September 11, the White House released the hold. Over the ensuing weeks, the committees issued a series of subpoenas to the administration for testimony and records. The administration complied with none of them, and on October 8, White House Counsel Pat Cipollone sent Speaker Nancy Pelosi a letter declaring a policy of total noncooperation with House investigations.
The president has maintained that policy since. At least 12 administration witnesses sought by the House have declined to appear, on White House instructions. Some current and former government employees have testified in compliance with subpoenas, but all of them did so contrary to White House directives. The House subpoenaed more than 70 categories of documents from executive-branch agencies, including the Departments of State, Defense, and Energy, and the Office of Management and Budget, and received exactly zero documents in return.
This categorical refusal is without precedent or legal justification. Past presidents have certainly resisted production of specific testimony or particular documents. But even then, they have done so by invoking judicially recognized doctrines such as executive privilege (which applies only to communications with the president’s closest advisers and must yield to a showing of need). No recognized privilege authorizes government-wide noncompliance with Congress. No president has ever presumed to order the entire executive branch to refuse to respond to congressional subpoenas, whether issued pursuant to oversight power or as part of a specifically designated impeachment investigation.