Lee H. Hamilton served in the US House of Representatives from 1965-1999, where he chaired both the Intelligence and Foreign Affairs Committees. He also chaired the House Iran-Contra Committee. Ken Ballen was the House Iran-Contra Committee's Staff Counsel. The opinions expressed in this commentary are their own. View more opinion at CNN.

(CNN) As Congress begins the most consequential series of investigations and oversight of a president and his administration since the Iran-Contra affair, important lessons from our congressional investigation of Iran-Contra can provide an essential guide.

Lee Hamilton

Ken Ballen

In January 1987, both the House and Senate decided to launch an investigation into the most significant presidential scandal since Watergate.

Mindful of our immense responsibility, we decided to adopt an unusual approach. Traditionally, congressional oversight involves requesting relevant records and witnesses and conducting public hearings. However, given the magnitude of the investigation and the importance of bringing it to a quick conclusion, the House and Senate Committees determined not to follow the usual norms of Congressional oversight.

Rather than only requesting documents, the Committees issued hundreds of subpoenas compelling document production. A document request can alert the subject of an investigation or even a witness to what papers could be destroyed or at least conveniently overlooked. A subpoena carries the force of law and compels compliance.

Some maintain that subpoenas should not be issued because they are a harsh and unnecessary step. Perhaps that might be true in some instances.

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