"I should've burned the tapes," President Nixon said later. But instead, his own recordings of White House conversations provided clear evidence of criminal wrongdoing - the "smoking gun" that proved Nixon guilty. By July of 1974, Congress had already voted to impeach the President over charges that he'd obstructed justice. When the tape surfaced in August, it proved conclusively that Nixon had done just that. Nixon lost all of his political support when the tape was released, and it was clear that he'd be found guilty if the impeachment trial was held by the Congress. To avoid the spectacle of a public trial, the President was forced to resign in disgrace.
Nixon had fought hard to conceal the tape, knowing it would prove his guilt and destroy his political career. Ten months before his resignation, Nixon had wanted to fire the independent special prosecutor who'd been appointed to investigate Watergate, since the prosecutor insisted on receiving copies of the tapes. Nixon's attorney general refused to perform the firing - and resigned in protest - so Nixon then asked the Deputy Attorney General to perform the firing. But the Deputy Attorney General also refused, and resigned in protest. Moving down the chain of command, Nixon now contacted the U.S. solicitor general, Robert Bork, who performed the firing.
Nixon had offered a compromise - that the tapes would be summarized by a U.S. Senator. His next gambit was to offer an edited transcript of the tapes (to the new special prosecutor who replaced the man he'd fired!) When the special prosecutor insisted on the tapes themselves, Nixon's lawyers filed a legal objection which went all the way to the Supreme Court. And the Supreme Court ruled against him, after which Nixon released the tape. Four days later, it had forced him to resign.
And what was on the tape? Proof that Nixon had secretly tried to block the FBI's investigation into a break-in to the Democratic Party's headquarters at the Watergate hotel. Just six days after the Watergate break-in, Nixon had met with his chief of staff, H.R. Haldeman, the tape showed, and discussed strategies for stopping the discovery that the burglars had been paid for with money from Nixon's re-election committee. "[T]he FBI is not under control..." Haldeman says, and "their investigation is now leading into some productive areas, because they've been able to trace the money...and it goes in some directions we don't want it to go." Haldeman's suggested the FBI should be led to believe that instead it was the CIA that was involved in the break-in by having deputy CIA director Vernon Walters. According to Haldeman, the President's advisors had decided that "the way to handle this now is for us to have Walters call [the head of the FBI] and just say, 'Stay the hell out of this...this is ah, business here we don't want you to go any further on it.' That's not an unusual development..."
"They'll stop if we could, if we take this other step," Haldeman says.
And Nixon answers: "All right. Fine."
Later Nixon confirms his understanding of the plan. "[J]ust say this is sort of a comedy of errors, bizarre, without getting into it, 'the President believes that it is going to open the whole Bay of Pigs thing up again...'" The CIA had been involved in a failed invasion of Cuba at the Bay of Pigs in 1961. Nixon's break-in team was led by a veteran of the Bay of Pigs operation - Howard Hunt - and one of the burglars had actually be involved with the failed invasion. But the break-in was not a CIA operation, and the tape proved Nixon was directing his staff to lie to the FBI.
But the real significance of the tape is it answered a crucial question about Watergate: "What did the President know and when did he know it?" The tape proved Nixon knew the illegal burglary was funded by legitimate campaign contributions from the very beginning - more than two years before the tape was finally released to the public. And the tape also proved Nixon knew about the massive cover-up, and had authorized White House officials to lie about it.
In the end, it was Nixon's own simple clumsiness which had proved his undoing. He'd connected himself to some highly illegal and objectionable activities - and then created a recording of himself discussing it with his staff! On August 9, 1974, President Nixon submitted a pre-trial resignation (though he was later pardoned by his successor, President Ford, for any criminal which might have been proven against him.) Nixon was always been a fierce politician, but ultimately he seemed to acknowledge his own responsibility in a farewell address. "Always remember that those that hate you don't win unless you hate them back," the President said, "because then you destroy yourself."