Sometimes, the most obvious things are worth pointing out. Richard Nixon -- born 100 years ago today -- was on a national ticket 5 times, and had he completed his second term would have held national office for 16 years. Not only that, but because his vice presidency and presidency were interrupted by Kennedy/Johnson, he first took national office in 1953 and resigned the presidency in August 1974, spanning over 20 years.
And of course Nixon was around longer than that; he became at least somewhat famous while in Congress. But Congress-famous isn't the same as national-ticket famous, or even close. I mean, Bob Dole was RNC chair for a while in the early 1970s, but I'm guessing that most Americans had never heard of him until Gerald Ford selected him as his 1976 running mate.
Nixon also almost perfectly lined up with the classic TV age, the era in which virtually every US household had a TV and virtually all of those TVs carried almost nothing but the (3) national networks, a public television station, and one independent channel -- so when the president gave a prime time speech or press conference, or when the national party conventions were on, odds are people were going to watch.
So it's not really surprising that Nixon would loom large, even without Watergate and resignation or anything else other than just running for and holding office when he did, for those who lived through that era. Including, of course, the historians and reporters who lived through that era -- and they help determine which politicians will loom large for the next generation or two. And of course in the event Nixon's career overall and his presidency in particular surely had a lot more drama than, say, George H.W. Bush's had.
I'll recommend, again, Garry Wills on Nixon, and of course the main sources for my Watergate posts: Fred Emery's Watergate; The Haldeman Diaries; and the tapes collected by Stanley Kutler in Abuse of Power. If you want to listen to White House tapes, you can go to the Miller Center; the Nixon Library has others. My latest Watergate post was a good one, just last night; and I'll also link to my quick version of what Watergate was, and to my overview of what Watergate tells us about the presidency.