Morning meeting in the Oval Office: The President of the United States, his chief of staff, and his chief domestic policy staffer, are considering the request for Secret Service protection from Senator Edward Kennedy of Massachusetts. Chastened by Watergate?
President Nixon: ...You understand what I'm talking about? You have anybody in the Secret Service that can you get to, do you have anybody that you can rely on?
Haldeman: Yes. We got several.
President Nixon: Plant one. Plant two guys on him [Kennedy]. This will be very useful.
Haldeman: What I was going to suggest is to give orders to the detail that they are never at any hour of the day or night to let him out of their sight.
Later that evening, The President, Haldeman, and White House aide Alexander Butterfield in the Oval Office
President Nixon: Now, the other thing that I want understood, have you covered the business on the Kennedy coverage? What man? Have you assigned a man to him?
Haldeman: Yeah. It's all in here, sir.
Butterfield: It's going to be in full force.
Haldeman: Don't put a big detail on him.
President Nixon: A big detail. Correct. Right. One that can cover him round the clock, every place he goes.
Butterfield: Everybody gets it. [Laughter] That too.
President Nixon: Just might get lucky and catch this sonofabitch and grill him for '76. He doesn't really know what he is getting into. We are going to cover him. He is not going to take no for an answer. Kennedys are arrogant as hell with these Secret Service. He can't say no.
Pretty clear: having done what they could to manipulate who the Democrats nominated in 1972, and having apparently paid little price even though things seemed to have gone as badly as they could, they might as well start manipulating the selection of the Democratic candidate in 1976.
And note again the level of detail that the president is involved in on these sorts of operations. Again, it doesn't prove anything about his involvement in other things and the lack of evidence of his involvement carries plenty of weight, too, but it's just worth thinking about when trying to assess the chances.