During the Watergate break-in, Frank Wills discovers there is duct tape on a door latch and removes it. In OTL, the tape was replaced by one of the burglars, but it was put on horizontally and it stuck out and Wills discovered it again, got suspicious, and called the police. If the tape had been replaced vertically, the Watergate Seven might not have been discovered and arrested.
Alternatively, the Fielding break-in in September of 1971 is botched and discovered. With the leaking of the Pentagon Papers in '71, Ehrlichmann organized the Plumbers and had them break into Daniel Ellsberg's psychiatrist's office in order to find incriminating evidence as to Ellseberg's mental state. They failed. Later, the Plumbers wanted to break into Ellsberg's psychiatrist's home but it wasn't approved by Ehrlichmann. The Fielding break-in wasn't known until the Watergate trial, but if it had been found out, G. Gordon Liddy wouldn't be recruited to CREEP. The Fielding burglary might have been traceable up to Ehrlichmann, but I don't think it could have gone all the way to Nixon.