What was the smoking gun of the Watergate scandal?

Answer 1

It was a taped conversation between President Nixon and his Chief of Staff Bob Haldeman, recorded a few days after the break-in, but by the time it was released Haldeman had been sacked.

In the recording, Haldeman had been suggesting to get the CIA to halt the FBI's investigations into to the break-in of the Watergate Building, and claim it was part of a national security operation. He warned that the FBI were investigating where the money involved in the scheme was coming from. Nixon agreed to the plan.

"Smoking Gun" is frequently used to describe a conclusive piece of evidence. It comes from a scene in a Sherlock Holmes story, in which Holmes and Watson rushed into the room where a murder had been committed, to find a man standing by the body with a smoking pistol.

Answer 2

In March, 1973, the Watergate burglars appeared before Judge John Sirica to be sentenced. Burglar and former CIA-agent James McCord wrote a letter to Sirica spilling the beans: he had perjured himself, the breakin was not a CIA operation, it led back to the White House. This letter opened the floodgates.