While more can always be said, LBJ's opponent in 1964 did a lot of self-inflicted damage, so I will reproduce my older answer on Did Barry Goldwater actually want to start a Nuclear War?

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"Want nuclear war" perhaps isn't quite fair; have an aggressive nuclear stance backed up by jingoist rhetoric, yes.

What really first got Goldwater into trouble -- and eventually depicted in the 1964 presidential race as nuclear-trigger-happy -- was the book ghost-written by L. Brent Bozell from the National Review entitled The Conscience of a Conservative. Bozell used Goldwater's speeches as a starting point and Goldwater approved the manuscript, so this was still "his", and it was only his name of the cover.

In the chapter "The Soviet Menace" Bozell wrote

A craven fear of death is entering the American consciousness.

This opinion was definitely also Goldwater's, and he doubled down in a later speech excoriating those he called cowards who he thought "would rather crawl on knees to Moscow than die under an Atom bomb."

He was most definitely an advocate for "tactical" nuclear weapons, and allowing the supreme commander to use them without presidential authorization. From a Der Spiegel interview:

There is real need for the supreme commander to be able to use judgment on the use of these weapons tactical nuclear weapons more expeditiously than he could by telephoning the White House, and I would say that in these cases the supreme commander should be given great leeway in the decision to use them or not to use them.

He had a proposal that NATO should have "its own stock of small, tactical nuclear battlefield weapons"; Goldwater in a speech stated "these are small, conventional nuclear weapons" that "are no more powerful than the firepower you have faced on the battlefield."

(This is not true and the Deputy Secretary of Defense incidentally called this description "dangerously misleading and totally inappropriate".)

Goldwater could emphatically state "peace" twenty times in a speech but also state

Choose the way of this present Administration, you choose the way of unliteral disarmament and appeasement.

Goldwater constantly gave the impression of "peace through overwhelming force". He joked about tossing a missile in the men's room of the Kremlin. He at one point noted the overwhelming numbers of US ICBMs vs. Soviet ICBMs, and stated

I want to make it unmistakably clear, then: In nuclear weapons, both strategic and tactical, no nation approaches us now and no nation will match us in the future.

Referring back one more time to The Conscience of a Conservative:

Moreover, it is clear that we cannot hope to match the Communist world man for a man, nor are we capable of furnishing the guns and tanks necessary to defend thirty nations scattered over the face of the globe. The long-overdue answer, as we will see later on, lies in the development of a nuclear capacity for limited wars.

It was not hard to paint a picture, then, of a nuclear warmonger. For the TV campaign, run by the ad agency Doyle Dane Bernbach, they decided to air nothing but 30 and 60 second spots and two 4-minute commercials. Previously, while short ads were used, campaigns were reliant on long speeches or documentaries interrupting regular programming. Doyle Dane Bernbach went for emotion, and in the famous "Daisy" ad -- with a girl annihilated by a nuclear blast -- did not have to even have to mention Goldwater by name.

There were other, less famous ads, like Confessions of a Republican and Girl with Ice Cream Cone, where the entire video shows a girl licking an ice cream cone with a voice-over. Here's part of it:

Do you know what people eventually did? They got together and signed a nuclear test ban treaty. And then the radioactive poison started to go away. But now, there is a man who wants to be President of the United States and he doesn't like this treaty. He fought against it. He even voted against it. He wants to go on testing more bombs. His name is Barry Goldwater.

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Mann, R. (2011). Daisy Petals and Mushroom Clouds: LBJ, Barry Goldwater, and the Ad That Changed American Politics. United States: LSU Press.

Matthews, J. (1997). To Defeat a Maverick: The Goldwater Candidacy Revisited, 1963-1964. Presidential Studies Quarterly, 27(4), 662-678.

Perlstein, R. (2009). Before the Storm: Barry Goldwater and the Unmaking of the American Consensus. United States: PublicAffairs.