... I have worked on several such inquiries, including the Church Committee’s investigation of the intelligence community in the 1970s, the Pike Committee’s investigation of the same, and the joint congressional investigation of the Iran-Contra affair in the 1980s. Some aspects of these investigations were carried out well; others were done poorly. Here are the pitfalls of past inquiries that should be avoided at all costs.

In 1975, the House Select Committee on Intelligence, chaired by Democratic Rep. Otis Pike of New York, began investigating whether the FBI and the Central Intelligence Agency were illegally spying on American citizens and whether the CIA was involved in coups abroad.

The purpose of congressional investigations is neither to impeach nor protect the president. Rather, it’s to preserve our democracy.

At one point, the committee informed the Department of State, where I was working as an attorney, that it had information indicating that Secretary of State Henry Kissinger had learned of a planned coup overseas but did not inform the head of state there because Kissinger wanted him assassinated. The committee planned to release the story the next day unless we could disprove it. The story was not true, and we stayed up all night pulling evidence together. But members of the committee who were politically opposed to Kissinger were so eager for this damaging bit of information to be real that we were barely able to convince them they were wrong.

The Pike Committee ultimately lost all its credibility when its draft report was leaked to the media. No committee chairman should want this legacy.

On the joint congressional investigation into the Iran-Contra affair, on whose staff I served, some Democratic members were convinced that President Reagan had knowingly violated a prohibition on arms sales to Iran and a statute limiting his ability to provide support to the Contras, who were fighting the Sandinista regime in Nicaragua. This conviction led to wistful thoughts of impeachment.

The Republicans sought to defend Reagan, resulting in much finger-pointing, bickering and an almost singular focus on the president’s role by the committee and the press, which in turn caused them to pass over other key details. ...