LBJ did exactly this.
Anecdote: in a journalism class, my prof recounted how LBJ’s press conferences consisted of his reading a prepared statement (distributed to media in advance) and that one day, a nice day, one reporter got his copy and decided to file his story based on the usual ho-hum release, and went off to have some fun.
Alas, when LBJ finished reading the release to the assembled reporters, he ad-libbed — “I shall not seek, and I will not accept, the nomination of my party for another term as your president.”
The absent reporter was fired and blackballed. And yet, he’s still a better reporter than the DNC shills working today.
March 31, 1968
Quotes:
Last week President Thieu ordered the mobilization of 135,000 additional South Vietnamese. He plans to reach—as soon as possible—a total military strength of more than 800,000 men.
To achieve this, the Government of South Vietnam started the drafting of 19-year-olds on March 1st. On May 1st, the Government will begin the drafting of 18-year-olds.
Last month, 10,000 men volunteered for military service—that was two and a half times the number of volunteers during the same month last year. Since the middle of January, more than 48,000 South Vietnamese have joined the armed forces—and nearly half of them volunteered to do so.
....
With America’s sons in the fields far away, with America’s future under challenge right here at home, with our hopes and the world’s hopes for peace in the balance every day, I do not believe that I should devote an hour or a day of my time to any personal partisan causes or to any duties other than the awesome duties of this office—the Presidency of your country.
Accordingly, I shall not seek, and I will not accept, the nomination of my party for another term as your President.