As mentioned by the other posters Nixon's own arrogance was probably his downfall. Couple arrogance and paranoia together and it is not a good combination. Unfortunately for Nixon his entire Presidency is remembered only for the Watergate break-in.
All good answers and insights which should give you plenty to think about as you write your paper. In addition to the aforementioned arrogance (both personal arrogance and the arrogance of position and power), it seems to me there was also at least a hint of paranoia. If he had been as confident as he appeared, there would have been no need for such actions. He clearly surrounded himself with like-minded people, as so many in power tend to do, and there were no checks and balances to address the issues of accountability and honor and ethics and morals. If they'd had even a small contingent of truly principled people in the Nixon Administration, the entire ugly episode might have been avoided.
There are many events in history that are not proud ones for America, but Nixon is the not the only US President to think he can get away with things just because he is the President. Jimmy Carter, Bill Clinton, and even Barack Obama are among those who believe they are above the law. Nixon was full of charisma and charm in front of the cameras so that the people thought he was what he presented to us...his recorded tapes full of profanity and racist remarks prove otherwise ...and when people learn to recognize that a good looking face and a nice smile doesn't equal an excellent choice for leadership, the better off we will all be, and the better we will get at choosing leaders who are really going to work for the good of the country.
I think a quote from Richard Nixon during his David Frost interviews says it all. He said, "When the President does it, that means that it's not illegal." This a view of the Imperial Presidency, the belief that the presidnt has the final say in what goes on in this country. I think Nixon really believed this and that he believed that he was not doing anything wrong.
Nixon obviously felt that his position as President gave him the freedom to bend and break laws with which he was not comfortable. He made the Presidency his personal throne, and perhaps no other commander-in-chief felt that he was immune to the laws that governed others. In the end, it was his own personal human character flaws that corrupted him.
Other editors have highlighted the fact that, sadly, the Watergate Scandal need never have been - it represents a character failing on his part. Unfortunately it is not America's brightest moment but it does again provide another example of power corrupting. As Lord Acton said, "Power corrupts, and absolute power corrupts absolutely." Paranoia and the fact that he was a very controlling president resulted in this well known case.
Richard Nixon's life is a story made for a movie, or better yet, a modern-day tragedy. Having a troubled childhood, Richard was raised by a somewhat abusive father and a controlling mother. Some historians have believed that as a result of his childhood, Nixon had a drive to succeed, to prove himself; certainly after his venomous battles with the media, he felt that he had to appear good while using any tactics to win. After Nixon graduated third in his class from Duke University Law School, but failed to procure a position in a New York law firm, his antipathy for the "eastern establishment" began. By 1947, however, Nixon proved his expertise in establishing foreign diplomacy. For this reason, he was asked to run as Vice-President with Dwight D. Eisenhower. He was highly successful in foreign affairs and ran the presidency well when Eisenhower suffered a stroke.
After Richard Nixon was leading John F. Kennedy in 1960by 11 points before the first televised debates, but lost, by the narrowest of margins, the presidential election because his lead plummeted after the debates on TV, he went on to run for governor of California in 1962, but lost to Edmund G. Brown. Disgruntled with the "liberal press" whom he felt persecuted him, Nixon suggested that he would drop out of public life saying to the media, "You won't have Richard Nixon to kick around anymore."
Nevertheless, he was nominated for president and won against Hubert H. Humphrey in 1968 because George Wallace of Alabama, a third-party candidate, drew many votes away from Humphrey. During his first four years, Nixon was successful, especially in foreign affairs as he signed an agreement with the Soviet Union in which USSR promised to reduce nuclear weapons. For a time, he also helped reduce inflation. However, throughout his political career, the liberal press hounded him and he became susceptible to lashing out at various journalists, aggravating the situation. (He suspected some in his cabinet as treacherous and providing information to the press.)
So, because of the antipathy between him and the press, and because of his past losses, Nixon ran a rather closed government and felt that he could take no chances and could not rely on the fickle polls. He allowed the Watergate break-in because of his paranoia of losing even though he had a lead, always remembering another loss that he felt he should not have suffered. So, to defend himself, he wanted as much evidence as he could glean from his opponents. This all was unnecessary as he won the election by a large margin. Nevertheless, his arrogance and a fear of openness with the press/media who had previously fallen upon him often with petty comments about his wife and other privte matters were the tragic flaws that clouded his reasoning and brought about his resignation.
What's more, the break in was completely unnecessary. He would have won the 1972 election handily, even if he hadn't resorted to Watergate or any of his other election antics, spreading rumors about his opponent, using CIA agents to disrupt his opponents campaign rallies, etc. This, again, proves that Nixon wasn't completely in touch with political reality in the US at that time.
There was also an arrogance about him, perhaps simply brought about by the power a man in his position wielded day to day. He believed that if he lost the election somehow, the American people would not have the leadership the country needed, so he had to cheat to win, to save us from ourselves. I think there was actually a part of him that was really frustrated Watergate would be pursued so doggedly, as though everyone should have realized it was just for our own good.
Presumably Richard Nixon caused the Watergate Scandal because of some defect in his personality. If he had been a completely rational person, he would have realized that the break-in could not possibly cause him to lose the 1972 election. He could have just told the truth -- that these were people doing stuff without his consent or knowledge.
But Nixon's personality was more controlling and suspicious (paranoid?) than that. He felt, therefore, that he had to cover up the incident. This involved him personally in the scandal and made it much more serious than it would otherwise have been.
Presidential scholars often say Nixon ruined his presidency and his legacy because his personality was just too paranoid and controlling.