Not sure what you mean by "pre-emptive military actions against the communists?" He had anti-Communists murdered; undermined anti-Communist Governments in the Third World; and, as others have cited, advocated the immigration policy his brother put through in 1965, which favored those with no historic ties to Americans, over those seeking to come from traditional sources of American descent!
His Secretary of State sought to out-do the Communists in undermining the cultures of other nations. Is that what you consider "pre-emptive?" It was a clear violation of principles of the "Law of Nations," recognized for over two hundred years. (And see American Foreign Policy.)
Yes, he did have writers who could write speeches full of pretty slogans. That does not excuse his efforts to move America to the Left.
Bay of Pigs, Cuban Missile blockade.