On Wednesday, Rep. Adam Schiff of the House Intelligence Committee said that he believed a special commission was needed to look into possible ties between the Trump campaign and Russia. Republican Sen. John McCain and former Vice President Joe Biden have also called for a special committee, while the New York Times editorial board and others have called for a special prosecutor.

But as calls mount for such an investigation, it's worth remembering that those two suggestions serve different purposes — and that history shows that, while they exist for very good reasons, it's important to use them judiciously.

First off, a special prosecutor — a role that has gone by various names over the years — goes after a specific crime on behalf of the Department of Justice, whereas a special commission or select commitee investigates and holds hearings under the aegis of Congress. (Committees and commissions have existed pretty much as long as Congress has, and “select” just means that it’s created temporarily for a specific purpose, so a select committee can also exist with a non-investigatory purpose.) As the Congressional Research Service explains in its overview of the subject, Congress has the authority to establish committees and commission to investigate "misconduct, mismanagement, or any other malfeasance relating to the officers and agencies of the executive branch of government," but actual law enforcement must come from the Department of Justice. The reason for the "independent" or "special" part is that the Department of Justice is itself part of the executive branch, so things get tricky if it has to investigate a crime possibly committed by someone who is also at that level of government.