Secretary of Defense James R. Schlesinger

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Go back in time to the summer of 1974 when the country was waiting on pins and needles to see what would be the outcome on the effort that was being made to separate Richard M. Nixon from the Presidency of the US. I was among those concerned about whether he would go quietly. I recall reading a story in the paper that said that the Secretary of Defense, James Schlesinger sent a memo to the Joint Chiefs of Staff directing that no orders should be executed unless they came through the chain of command. That is, through him.

Some folks would say, of course, that is what he should have done.
Some folks would say that he was exceeding his authority.
Some folks would say that he should have counted on the Generals to refuse any inappropriate order.

It seems to me that Secretary Schlesinger acted in an extremely courageous manner with that action.
Perhaps it was not necessary. But that is the kind of thing that you can never be sure was not necessary.
Schlesinger countered any temptation that Nixon might have faced to try to use the military to continue his presidency.
Most importantly, I think, he gave the generals cover in the event they had been obligated to refuse an order from the President.
He took the peril of what might have been labeled their treason onto his own shoulders.

Now, I cannot find a reference to that memo.
But I did find the following, which is close.

August 22, 1974: Pentagon, Joint Chiefs ‘Kept Watch’ on Nixon to Prevent Coup Attempt, Newspaper Reports

The Washington Post prints a small, almost-buried story entitled “Pentagon Kept Watch on Military.” The relatively innocuous headline conceals a potentially explosive charge—that during the final days of the Nixon administration, Defense Secretary James Schlesinger and the Joint Chiefs of Staff had “kept a close watch to make certain that no orders were given to military units outside the normal chain of command.” The article, careful in its word choices, says the extraordinary alert was “based on hypothetical situations that could arise during a period when President Nixon’s hold on the presidency was not clear.… Specifically, there was concern that an order could go to a military unit outside the chain of command for some sort of action against Congress during the time between a House impeachment and a Senate trial on the impeachment charge.” Pentagon sources say no one has any evidence that any such action was being contemplated, but steps were taken to ensure that no military commander would take an order from the White House or anywhere else that did not come through military channels. The implication is clear: Pentagon officials worried that Nixon might use certain elements of the military to stage some sort of coup. Schlesinger gives the story “legs” by issuing the following non-denial: “I did assure myself that there would be no question about the proper constitutional and legislated chain of command, and there never was any question.”