Nixon and Haldeman are back in the White House, which means that the tapes are rolling...and, in late morning, the famous 18 1/2 minute gap tape.
Here's what we know: the tape was almost certainly deliberately erased -- by Haldeman, by Nixon, by Nixon's secretary Rose Mary Woods, or possibly by someone else. Nixon says that they talked about Watergate only in terms of public relations. Haldeman, however, says that they talked about the substance, and reconstructs Nixon saying: "Colson can talk about the president, if he cracks. You know I was on Colson's tail for moths to nail Larry O'Brien on the [Howard] Hughes deal."
That's pretty bad, if that's what was really said, and certainly would be a reason to erase the tape. On the other hand...well, let's do it this way.
The conversation could have been about something which was unproven at the time, but is now clearly on the public record. That could include, for example, something as basic as Nixon's involvement in the cover-up from the beginning. It's certainly plausible that Nixon (or Haldeman) could have come across this tape when it was subpoenaed, realized that it was incriminating, and erased it even though there was, eventually, nothing unique about it. I think that's the most likely possibility.
The conversation could have shown something that we suspect or wonder about, but don't know. Obviously, the big one would be if there was anything about Nixon having prior knowledge of the break-in. But there are lesser and still major possibilities, including clear evidence that Haldeman knew about the break-in(s) before the fact.
And then there's the unknown unknown: that there was some other bombshell they talked about that successfully remained secret. Remember, everyone that week was busy shredding files and destroying evidence; I've always thought that it was plausible that there might be some completely unknown Plumbers operation. Would Liddy have told, even now? I don't think this one is especially likely, but I wouldn't rule it out.
Anyway, as to the first possibility -- they talked about stuff that they talked about multiple times, but that particular one was subpoenaed -- Nixon and Haldeman spoke again later that day, and that one was taped (and was one of the tapes that wasn't released for a couple decades). In it, Haldeman briefs Nixon on the break-in itself, including several details the FBI didn't have yet; that Hunt is (again) disappeared and "can undisappear if we want him to. He can disappear to a Latin American country"; that McCord and the Cubans may develop a cover story that they were doing it on their own for political reasons; and Haldeman and Nixon both try out some of their own spin. It is of course clear that there's a cover-up in progress.
There's just too much to get to today, and I can't get to it all. Quickly, some of the highlights: The White House and CRP people meet, separately and together, to coordinate their responses. John Dean meets with the Attorney General and with Henry Peterson, the assistant attorney general who will be overseeing the case, in order to see where they are and to push to limit the investigation to just the break-in itself. The re-election committee folks meet with Liddy, and begin to think about paying off the arrested men; there's also a phone call later, between Haldeman and Nixon, in according to Haldeman (but not Nixon) the president raises the possibility that money could be raised for the burglars. Oh, and the DNC and O'Brien file a civil suit over the break-in, which raises the question of how badly discovery would damage them.
One more thing. Several of the various conspirators are fascinated to discover how many of the people involved in the break-in have CIA ties of some kind (McCord, Hunt, some of the Cubans), and the seed is planted that perhaps that might be useful; indeed, Nixon himself may have raised it at this point.
So the cover-up is starting to come together, but it's still early.
Meanwhile, if you really want more from today, you can read the transcript of a Nixon conversation with Chuck Colson. Nothing startling, but it does give you a sense of how the regarded it at that point.