Why Nixon was obsessed with certain break-ins was something of a mystery that resulted in speculation similar to that of guessing who the real Deep Throat was for decades. He had even proposed bombing the Brookings Institute, which seemed rather extreme. Intelligent students of Nixon tried to tie the Watergate and Ellsberg's psychiatrist's break-ins with Brookings and the break-in at the Chilean embassy with little success for years. As it turned out, the psychiatrist's office was not directly related to the others.
In 2012, Lamar Waldron provided the answers in his extremely well-documented "Watergate: The Hidden History (Nixon, the Mafia, and the CIA)." Castro had released a report on the CIA's attempts to kill him, which documented that VP Nixon had been the moving force in getting the CIA to enlist the help of the mob to kill Castro. One copy of the report was believed to be in the Chilean embassy. Another was believed to be at the Democratic headquarters at the Watergate (this was Ted Kennedy's copy). A third at Brookings.
Yet another extremely important book is David Brinkley & Luke Nichter's "The Nixon Tapes: 1973." This is the second of two books of transcribed Nixon tapes. It was published in 2015. It documents that Nixon's primary concern in initially covering up Watergate was his fear that the Huston Plan would be exposed. This continued to be his greatest fear. Like many at the time, I was outraged when Ford pardoned Nixon. However, looking back, I recognize that Nixon could have won any of the obvious cases against him .....unless he was charged with approving the Huston Plan. And that brings us full-circle, as this plan, in large part, resulted in CREEP's unethical and illegal activities in the 1972 Democratic primary season, etc.