Many of the lingering security problems that we face today are directly the result of Truman's soft policies. He may have been the Democrat who was toughest on Communism, but he wasn't nearly tough enough.
Ouch! Cuban Revolution 1959: Castro came to power. Eisenhower's watch.
Actually, Truman was responsible (with Dean Acheson, his Secretary of State,) for the poicy of Containment, aiding the Greek government against a communist takeover immediately after WWII. He was an anti-Communist who was stuck with the deals that FDR had made with Stalin regarding Eastern Europe after WWII.But he did come up with the pre-eminent policy of the Cold War, which was to contain Communist expansionism
Of course this meant fighting them in the Korean peninsula, and later, in Vietnam, as well as in various proxy wars fought by us and our allies in Malaysia, Indonesia, Central America, Southern Africa, and so forth.
The unfortunate fact is that some conservatives are unwilling to give a Democrat or liberal credit where credit is due. The question is what was Truman's overall record fighting communism not particular errors he might have made. His overall record was outstanding. Yesterdays Dems are not the same as todays as Horowitz, hardly a liberal apologist, has pointed out.