A 50-Year Memory: He Wouldn't Run Again.

March 31, 1968:
"I shall not seek and I will not accept the nomination of my party as your President."

I was on the Northeast Extension of the Pennsylvania Turnpike. Several of us were returning to school after spring break. I seem to remember it was  a foggy evening as we listened to the president's address to the nation. Like most, we were stunned and elated.

Tom Wicker reporting in the New York Times after the speech described Johnson as talking about the progress made in his years as president. But they

"must not now be lost in suspicion and distrust and selfishness and politics. ...I have concluded that I should not permit the Presidency to become involved in the partisan divisions that are developing."
And so it was that the man who won the biggest political landslide in American history, when he defeated Senator Barry Goldwater of Arizona in the Presidential election of 1964, renounced the idea of a second term. (Link)

LBJ knew he was losing support. McCarthy had shown Johnson's vulnerability. Bobby Kennedy was waiting in the wings. He was president of a deeply divided nation. He didn't know it at the time but it was very quickly going to get much, much worse.It was stunning, but soon to be overtaken by events in Memphis, Los Angeles, and the streets of Chicago and Prague.

One of the most chaotic and challenging years was just beginning.