The Watergate excesses (using the term inclusively to include things like "dirty tricks") were unnecessary. Nixon was a shoo-in to be re-elected. If Ed Muskie had been the Democrat nominee, he would have carried a few more states than McGovern did, but it would still have been like Eisenhower's victories over Stevenson. But Nixon and CREEP wanted a landslide and that tripped them up.
The Obama/Hillary/Comey/Brennan conspiracy in 2016 was different--there was a real contest and the conspiracy was meant to ensure the right person won.