While it is not known if President Nixon knew about or was involved in ordering the break-in at the Watergate Hotel, it is known that he and White House Chief of Staff H. R. "Bob" Haldeman were recorded on June 23, 1972, discussing using the CIA to obstruct the FBI's investigation of the Watergate break-ins. He even asked the CIA to slow the FBI's investigation, claiming national-security risks. These revelations led to Nixon's resignation when it became apparent that he would probably be impeached.
When burglars were caught on June 17, 1972, breaking in to the Democratic National Committee headquarters at the Watergate Hotel-attempting to place wiretaps and steal secret DNC papers-it didn't help their case that one of them had the phone number of the White House office of the Committee to Re-Elect the President.
Nevertheless, the White House denied any involvement or knowledge of the break-in. Nixon did so, personally, as well. Addressing the nation two months later, he said not only that he was not involved, but that his staff wasn't either.
Three months after that, Nixon was re-elected in a landslide.
Impeding the Investigation
What Nixon did not tell the nation during his speech was that as early as two months before, less than a week after the burglars were caught, he was secretly discussing how to get the FBI to back off of their investigation. Haldeman, can be heard on White House tapes specifically telling Nixon that the FBI investigation was going “in some directions we don't want it to go.”
As a result, Nixon decided to have the CIA approach the FBI to take the investigation off their hands. The sentiment Haldeman shared with Nixon was that the CIA's investigation could be controlled in ways that the FBI's could not.
As the investigations went on, Nixon's fear mounted that the burglars would start cooperating-and would tell everything they knew.
On March 21, 1973, it was later revealed, the secret White House recording system taped Nixon discussing with White House Counsel John Dean how to raise $120,000 to pay off one of the burglars, who was demanding cash for his continued silence.
Nixon went on to explore how they could secretly raise as much as a million dollars to distribute to the burglars-without the money being traced back to the White House. Some cash was, in fact, distributed to the conspirators as early as just 12 hours after that meeting.
The Nixon Tapes
After investigators learned of the existence of the tapes, Nixon refused to release them. When the independent counsel investigating Watergate refused to relent in his demands for the tapes, Nixon had the Department of Justice replace him.
Only after the Supreme Court intervened to order the tapes released did Nixon comply. And even then, there was what has now become famous as the 18-1/2 minute gap. The tapes proved conclusively Nixon's knowledge of and involvement in the cover-up and, with the Senate preparing to impeach him, he resigned just three days after the tapes were released.
The new president-Gerald Ford-quickly turned around and pardoned Nixon.
Thanks to Watergate.info, you can actually hear what's referred to the smoking-gun.