After President Richard Nixon was forced from office in 1974, congressional investigators discovered what they believed was the full extent of his use of the FBI and the CIA to engage in domestic spying. In that pre-digital era, the spying consisted of listening to telephone calls, opening mail, and using undercover agents to infiltrate political organizations and, as we know, break into their offices. Nixon claimed he did this for the protection of national security. He also claimed he was entitled to break the law and violate the Constitution. "If the president does it, that means that it’s not illegal," he once famously said.