There are, it turns out, two plane crashes which make a great deal of difference in how the Watergate story played out.
The first one actually had happened back on October 16, a month before the election. The plane carrying Democratic House Majority Leader Hale Boggs (and Member of the House Nick Begich disappeared over Alaska. The plane, and those aboard, were never found. The tragedy elevated Tip O'Neill to the number two spot among House Democrats; O'Neill saw, perhaps sooner than anyone else or at least anyone else in a position to do anything about it, that Watergate could cut short Nixon's presidency. Early on, O'Neill started telling key Members to be ready for impeachment; as Jimmy Breslin reported (according to Emery), they thought he was nuts. It's hard to draw direct lines, and O'Neill had been the Democratic Whip anyway, but certainly his elevation wasn't good news for the president.
Now, on December 8, the second tragedy: Dorothy Hunt, the wife of at the time indicted Watergate criminal E. Howard Hunt, was killed in a commercial airline crash. She was carrying $10,000 in cash. Dorothy Hunt had been active in the last couple of months in the successful efforts of the indicted men to get the flow of hush money re-started. Her death is devastating to Hunt, and comes at a key time in the sequence from the cover story holding to the unraveling of the cover-up.
Watergate on this date is back in Haldeman's diary, which has been mostly devoted during December to Vietnam, and to some extent with personnel changes for the second term. Note that the president comes back again and again to the need for the Dean report, which would prove their innocence:
Got back into the Watergate/Segretti thing, wanted to be sure that he gets the Dean report. He thinks Dean ought to talk to the press rather than [press secretary Ron] Ziegler, to give the summary on it. Wants to have a meeting on that subject the first of the week.