Lily-livered or not, it was a fact of politics 1946 to 1989. And JFK, among others, also certainly acted on it.

He probably needlessly jeopardized the world by not agreeing to Khrushchev's publicizing the trade which the Cuban missile crisis was defused---the missiles in Cuba for US Jupiters in Turkey. Because the trade was not publicized, Khrushchev appeared weak to other Soviets--and lost power soon thereafter.

JFK also made a big issue in the 1960 campaign of a "missile gap" which he knew did not exist, since he had been briefed.