Congress has no authority to question or investigate the President's security clearance decisions.
Updated: Apr 6, 2019
Security clearance decisions are an Executive Branch function. They flow from the President's Article II powers in the Constitution. A Congressional "oversight" role of this Executive Branch function does not exist.
The decision this week by a House of Representative Oversight Committee to hold hearings into the Trump administration White House security clearance adjudications is completely flawed. The President as the head of the Executive Branch of the federal government has the exclusive authority to grant or deny security clearances. This flows from the President's role as Commander in Chief and other responsibilities under Article II of the Constitution. Unsurprisingly, the White House Counsel's Office has refused to provide any information or documents to the House concerning these issues, pointing out that the House has no authority in this area at all. There may well be many things the Trump administration is doing that the House of Representative can investigate as part of its Congressional oversight function, but this isn't one of them.