As might be expected, the 1940 campaign for President of the United States was dominated by one issue above all others - World War II. There were essentially two camps, isolationists and interventionists, in both the Republican and Democratic party. Whether a candidate supported involvement in World War II, either indirectly through material support of Germany's opponents through programs such as the Lend-Lease act, or directly through a military confrontation with Nazi Germany and its allies, had become the most important issue of the day.
Roosevelt himself had been initially reluctant to run for his third term, only deciding to do so as Germany invaded Western Europe in the spring of 1940. He felt that he alone had the experience necessary to lead the United States. He was unintentionally emboldened in this belief by two Supreme Court decisions. The 1936 Supreme Court decision in U.S. v. Curtiss-Wright Corporation et al, which challenged the constitutional legality of an embargo on the sale of weapons to Bolivia and Paraguy, who were then at war, ruled that the office of the President had an inherent authority in foreign affairs and that it did not require an act of Congress to exercise this authority. This was followed a year late by U.S. v. Belmont, which dealt with the legality of the president acknowledging the legality of Soviet seizures of private businesses owned by Russian refugees living in America. The majority verdict in that case found that international relations could take place outside the realm of treaties, and thus didn't always require participation of the Senate.
With World War II rapidly expanding and the office of President being more powerful than ever in the realm of foreign policy the Republican National Convention selected an extremely unlikely candidate in the form of Wendell Willikie. Willikie was a former supporter of Roosevelt, but had fallen out with the president when Roosevelt sought to create the Tennessee Valley Authority, which would compete directly with the Commonwealth & Southern Corporation, a utilities holding company for which Willikie worked as legal council. When Roosevelt sought to break the monopoly of companies such as C&S in 1935 it only pushed Willikie further in opposition of Roosevelt. He remained a registered Democrat until 1939. He had gained a lot of popular support during that time as the businessman with a heart, pushing back against what many saw as Federal overreach in the New Deal program. As he was sure that Roosevelt would run for a third term, he decided that the Republican party represented his best odds at securing the presidency.
Coming into the 1940 Republican National Convention Willikie was the only serious candidate who fell in the interventionist camp. With Roosevelt already having managed to gain momentum for interventionism, appointing two Republican interventionists to the positions of Secretary of War and Navy Secretary, and Willikie having massive popular support, he managed to swing the convention in his favour in spite of coming into the convention with relatively few delegates backing him. With news coming in that France had fallen right in the middle of the Republican convention the political fate of the isolationists was sealed.
Although both Roosevelt and Willikie ran as interventionists the former attacked the latter on his lack of political credentials in general and foreign policy experience in particular, repeatedly referring to him as "a dangerous experiment." While Roosevelt was popular due to his success in fighting back against the Great Depression, and his successful acclaim to foreign policy experience, he did have critics who considered him a warmonger, who pushed for support of the Allies beyond what the United State's neutrality would allow and thus push America into World War II. There were also many critics for the fact that he broke with the two term tradition. George Washington had set an informal precedent by not running for a third term. Although certain American presidents, most notably Theodore Roosevelt, FDR's distant cousin, had sought third terms, Roosevelt was the first to actually get elected to such. His leadership in World War II meant that there were relatively few public challenges to his decision to run for a third and fourth term, but after his death the twenty-second amendment was passed specifically to prevent any other president from repeating his feat.
In the 1944 elections the Republicans accepted the fact that they would only have a limited chance to take the White House but they had their hopes set on taking the House and the Senate. They came up unexpectedly short here. Roosevelt secured less of the popular vote than he had in 1940 but he nonetheless carved out a victory on broad popular support in many different areas of the United States. The shock of Roosevelt running for (and winning) a fourth term wasn't nearly as big as the shock when he ran for his third term, and with the United States in the middle of the war, Roosevelt's critics were a lot less vocal.
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