It never was conclusively shown one way or the other, as far as I could tell, if Nixon knew about the break-in in advance. Remember the June 17 break-in was the second break-in, intended to replace a tap that was not working. John Mitchell was in charge of people involved in Watergate, and was also having frequent conversations with Nixon. Nixon had a reputation for micro-managing. There were conversations between the two of them which were never released, as far as I know, so it's possible that Mitchell told Nixon...but perhaps not, to provide "deniability."
The other thing is the 18 1/2 minute gap...it's almost certain that it was erased by human action, and the official version of Rose Mary Woods doing it accidently was always very dubious. It may well have been Nixon himself who discovered that there was explosive material in that part of that tape and erased it himself...I believe there were handwritten notes (maybe Haldeman's) from that conversation which indicated that the topic of conversation was Watergate during the time period that the erased tape covered. We'll never know--those who might have known are dead now.
Well .. what we might or might not "believe" about this situation doesn't matter. What matters to me is that I will not just stand by and allow people to make misstatements about Nixon. Yes, he made a terrible mistake, but he knew how the vultures in the media would react. And .. at the time the media had much more power than they do now.