The Five Worst Presidents
#5 When He Was Good, He Was Good; When He Was Bad, Whoa: Richard Nixon
Richard Nixon is generally considered one of the worst American Presidents - impeachment and resignation tends to have that effect. But his foreign policy record is more mixed. His accomplishments are among the most consequential of the Cold War, in particular, his opening to China in 1971 and his efforts at détente with the Soviet Union. Considering that these had been his two overriding priorities upon taking office it's even more impressive.
Of course the ledger on the other side is pretty ugly. It took Nixon four years to wind down the Vietnam War (with tens of thousands more American dead as a result). This came after he and his top foreign policy adviser, Henry Kissinger, had scuttled a potential breakthrough only days before the 1968 presidential election (an act that to the less charitable might be considered borderline treason). His decision to bomb and then later invade Cambodia led to the ascendance of the Khmer Rouge and the death of a million Cambodians. He escalated the bombing of North Vietnam to get a final peace deal, which led to horrible civilian casualties; and then when that deal was reached his political problems at home over Watergate helped to undermine the case for continuing to support South Vietnam. There was also the deposing of Prime Minister Allende in Chile, Nixon's virtual nervous breakdown during the Yom Kippur War (although Kissinger's subsequent shuttle diplomacy paved the way for the Camp David Accords) and, the stain of Watergate badly undermined the US image in the world.
From the narrow perspective of US interests, Nixon had important successes and might even be considered an above average presidency; but with the fuller range of human consequences of his policies is considered it's much harder to give him a passing grade.
#4 The Overrated: Harry S. Truman
Harry Truman has in the nearly 50 years since he left the White House grown significantly in the estimation of both the public and many historians. To be sure, he deserves enormous credit for protecting and stabilizing Western Europe with the Marshall Plan and the creation of NATO. These are signal achievements but as historians from Robert Dallek and Walter Lafeber to Fredrik Logevall have suggested there is a pretty significant downside to Truman's presidency as well.
First there was Korea. An impulsive response to a cross-border attack that re-shaped American foreign policy. It was the final nail in the coffin of the more modest containment strategy proposed by George Kennan and by default enshrined the notion that the US had a responsibility to contain Communism wherever it showed its fangs. But while the decision to go to war can be considered a debatable one; the failure in rein in Douglas MacArthur's push to the Yalu River, which triggered a Chinese intervention is a disaster that can't be washed away (even by Truman's later decision to fire the general). Considering that more than 20 million North Koreans continue to live in terrible hardship today because of that decision only compounds the mistake.
Beyond Korea, the Truman Doctrine and its declaration that it was the "policy of the United States to support free people who are resisting attempted subjugation by armed minorities or by outside pressures" laid the groundwork for the limitless definition of US national interests that unfolded over the next 60 years. As Kennan would later note, it was one thing to contain Communism in Europe (a goal on which Truman succeeded). It was quite another to broaden that goal to the rest of the world. There is, as a result, a straight line between Truman's foreign policy choices and the war in Vietnam.
Then there was Truman's use of anti-Communist rhetoric for political advantage that turned what might have been a balance of power, geo-political clash into an ideological one. This, of course, also helped to politicize the Cold War in the United States and heightened the issue of anti-Communism. Indeed, few Presidents more flagrantly used foreign policy as a political punching bag as frequently as Truman.
Finally, ask yourself a counter-factual: how would the Cold War have unfolded if FDR had lived out his fourth term, rather than having the inexperienced Truman become the leader of the Free World? It's not hard to imagine that the tensions between the United States and the Soviet Union, so deftly handled by FDR during WWII, would have been minimized and a less militarist and dangerous conflict might have emerged. At the very least, as Robert Dallek points out even if superpower, ideological conflict between the US and Soviet Union was inevitable, Truman never really sought to find an alternative.