Watergate is an incredibly interesting period of political history that I feel is greatly misunderstood by many people today. It helps to think of the scandal not as a single 'event' but rather as a storm of linked occurrences that eventually reached a boiling point.
As you are probably aware, the Watergate scandal had its genesis when a group of individuals were caught illegally breaking into the Watergate complex, which at the time was the Democratic Party's national headquarters.
The exact purpose of the break-in has remained surprisingly nebulous, but generally it is assumed that the objective was to obtain political intelligence for use in the upcoming 1972 election. Jeb Magruder, who was deputy director at the Committee for the Re-election of the President and one of the main figures involved in the scandal, said in an interview that they wanted to get Larry O'Brien's (who was chairman of the DNC at the time) opposition research on Republicans.
The reason why this scandal was so catastrophic to Nixon, his senior aides, and his administration was largely because of the coverup that followed that also caused the revelation of the other 'horrors' that had occurred within the Nixon White House. For what it's worth, the generally accepted history is that Nixon was not aware beforehand and had certainly not ordered the Watergate break in itself.
Eventually, the money trail of the Watergate burglars led to the Committee to Reelect the President (sometimes ironically referred to as CREEP), which was linked to key figures of the Nixon Administration like John Mitchell who had served as Attorney General. CRP was involved in many legally questionable activities such as money laundering, maintaining slush funds, and many of its members eventually committed perjury when questioned about its activities.
To cut a very long story short (and skipping over some intermediate steps of this scandal), it eventually became known that Nixon maintained a taping system in the Oval Office, at his study in Camp David, and at the Eisenhower Executive Office Building. The existence of this taping system was revealed by Alexander Butterfield during his Senate testimony. These tapes were immediately subpoenaed but Nixon refused to comply by citing executive privilege.
Subsequently, after the special prosecutor Archibald Cox refused to compromise with Nixon over the tapes, Nixon ordered the Attorney General Elliot Richardson to fire Cox. He refused to do this and instead resigned. Then, Deputy Attorney General William Ruckelshaus was ordered to fire Cox. He also refused, so Nixon fired him. The next in line was Robert Bork, who did eventually fire Cox. This event is known as the Saturday Night Massacre.
Despite Nixon's best efforts, after the unanimous United States V. Nixon Supreme Court decision, he was eventually forced to hand over the raw tapes of his conversations. These tapes revealed a vindictive, petty, and rude President that contrasted strongly with his public image.
One of these tapes is the 'smoking gun tape'. This conversation caused his political support to completely evaporate. You can listen to this tape here. Essentially, Nixon agrees with Haldeman's plan of using the CIA to stop the FBI's investigation into the Watergate break-in under the guise of 'national security', a clear obstruction of justice. Furthermore, other tapes reveal more disturbing information of the coverup, such as Nixon's endorsement of 'hush money' to participants of the Watergate burglary. Also, other abuses of power such as using the IRS to audit Nixon's political enemies were also uncovered.
Facing certain impeachment on at least one count of obstruction of justice, Nixon resigned on August 9th 1974. Dozens of Nixon's top officials were found guilty of perjury, obstruction of justice, and conspiracy and subsequently many had to serve lengthy prison sentences. Nixon himself, of course, was spared such a fate by virtue of Gerald Ford granting him an absolute pardon.
This post is already rather lengthy, so I will stop here. But there are many layers to the scandal that I haven't touched on explicitly (such as the role of John Dean, the efforts of E. Howard Hunt to 'blackmail' the White House, Pat Gray's destruction of evidence, the role of 'Deep Throat', etc.)
It's truly difficult to succinctly tell you just how deep the malfeasance ran during Nixon's presidency. So many shady and unethical things were done by people who were extremely close to Nixon.
Here is just one example: this tape is a conversation between Nixon and John Ehrlichman, who served as Nixon's top domestic policy advisor. This conversation is fascinating (I have time stamped the URL at the most pertinent point). Nixon asks Ehrlichman if he had ever heard of a fake letter from JFK to President Diem. Ehrlichman not only says that he is aware of it but that Charles Colson (one of the President's closest advisors) was the driving force behind this fabricated cable.
Nixon is astonished. I think this tape helps to show just how deeply the unethical behaviour festered in the White House. The President's closest associates were involved in blatantly illegal and immoral activities. We can only wonder what happened in the 18 and a half minute section of the tapes that was suspiciously erased.
For further reading, I would recommend books that go into detail of the Nixon tapes. For example Abuse of Power by Stanley Kutler examines the Watergate coverup and other behaviour of the Nixon White House by persuasively using the President's own words.
Hey there!
Not to preclude further discussion, but you may be interested in these four posts by /u/The_Alaskan which discuss Watergate and its implications.
Now, all of these have a certain level of assumed knowledge about Watergate, so I may getting things the wrong way around by recommending you our further-reading list before providing an actual discussion of precisely what Watergate was! However, you'll hopefully find them interesting reading, and either /u/the_Alaskan or another user will, with any luck, be able to provide you with a succinct discussion of the crisis itself here.
Edit: And thank you to /u/extremeftw for your explanation!
I know this sub prefers in-depth answers, but I'm going to try for a succinct answer here, because I think it's actually helpful.
In the simplest terms, Watergate was the revelation of massive corruption and ethics violations in the Nixon administration.
How it was revealed: there was a break-in at the Watergate hotel in January of 1972 in Washington, DC that was foiled. The Democratic National Committee's headquarters were in the hotel, and the break-in was performed by operatives working for Nixon to steal materials from the DNC and tap the DNC's offices. The purpose of this work was for the Nixon re-election campaign to gain an advantage over the Democratic party's campaign in the 1972 election (which happened in November). The break-in was discovered while in progress and the perpetrators arrested.
It is very important to understand that this is not the entirety of the "Watergate scandal". This is the visible tip that revealed the body of the iceberg. The body of the iceberg is the real scandal.
After the break-in there was an attempt at a cover-up, which actually made it more evident that the seriousness of the issue was greater than it seemed, and led towards uncovering the vast expanse of corruption in the Whitehouse that eventually led toward Nixon's resignation.
What was the nature of that corruption? It was multi-fold. One aspect was that the president was using the power and facilities of the federal government for his own political gain, to persecute his political enemies, and to undertake political "black bag" operations. The Watergate hotel break-in itself was an example of this, as it employed CIA operatives who committed crimes in service to the work of facilitating Nixon's re-election. But there was much more, Nixon used the IRS, FBI, and CIA to hound his personal and political enemies. He used his re-election campaign finances as a "slush fund" to pay bribes or, really, for whatever personal purpose he desired.
To reiterate, Nixon subverted the powers of the federal government to work in his personal interests directly, even in violation of the law. This is the core of Watergate. Nixon turned the United States government into a corrupt banana republic. He used the government not to serve the people but to serve himself. To keep himself in power. To punish his enemies. To flagrantly ignore the rule of law in service to raw executive power. These things are directly in opposition to everything the Constitution was created for. Nixon was only in office a few years and yet he managed to corrupt the system to such a degree that he bent it significantly toward tyranny.
That is why Nixon is so vilified. Because he shattered the illusion and the hope that America was above such petty corruption, and tarnished forever both America and the office of the President.
Related question: has any effort been made to "unerase" the mysterious 18-minute gap in the Nixon tapes? Is this technically feasible?
I am late to the party. But here is a pdf of an interview with two FBI agents who worked the case. My uncle was their supervisor.