There were several isolationists who could have won in 1940--among Republicans, Taft, Vandenberg, and Dewey (the latter two as yet unconverted to internationalism), indeed most GOP presidential candidates other than Willkie. Among Democrats, if FDR didn't run, Burton Wheeler is a possible, though hardly likely, nominee. But none of these men were "pro-Nazi" either publicly or privately. Indeed, it is surprising how few of the isolationists even professed indifference to Britain's plight (let alone Nazi sympathies). To quote an old post of mine on alternatives to lend-lease:
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It is sometimes assumed that the enemies of lend-lease were indifferent to whether Britain was defeated (or even actually wanted a German victory). Actually, most of them would have denied this; the great majority of them professed to want to help Britain in *some* way, but in a way less likely to get the US into the war, or involving better financial/strategic terms for the US:
"Each lend-lease opponent, it seemed, had a different alternative to FDR's comprehensive legislation. Merwin K. Hart, president of the New York State Economic Council and an arch-rightist, merely called for the continuation of cash-and-carry. Others spoke in terms of a straight loan, with sums ranging from $2 to $10 billion. Taft for example suggested offering $2 billion in loans to Britain, Canada, and Greece.
"Others considered outright gifts. Edwin Johnson would authorize the president to turn over $2 billion worth of munitions to Britain for 'testing.' Herbert Hoover would give Britain all the defense material the United States could spare and some $2 to $3 billion to make other purchases. The U.S., said Senator George Aiken, should donate outright the larger part of a $2 billion lend-lease appropriation in the form of materials to Canada. General Wood suggested that Britain exhaust its U.S. resources, after which it would receive gifts or loans of planes, artillery, and tanks, all carried in Britain's own vessels. More moderate than some anti-interventionists, Wood did favor selling American merchant ships to Britain, provided the U.S. merchant marine would not be crippled in the process.
"Several anti-interventionists proposed bargaining over certain British colonies within the Western Hemisphere. The British, said the *New York Daily News*, should simply give the United States its pick of sites as well as other 'conveniently located pieces of the empire.' Wood spoke of the transfer of Newfoundland or British Honduras. [Hamilton] Fish's eye was on the West Indies. Representative Melvin J. Maas proposed an amendment enabling the U.S. to purchase all British possessions in the Western Hemisphere, with the obvious exceptions of Canada and Nova Scotia.
"Other goods and concessions were sought. Congressman William J. Barry (Dem.-N.Y.) noted such British raw materials as manganese, chromium, tin, and nickel. Nye wanted Britain's commercial shipping. Wiley desired revision of the Hay-Pauncefote treaty (1901) with Britain, which provided free access to the Panama Canal to ships of all nations on equal terms.
"A few anti-interventionists used the debate over lend-lease to suggest total impartiality in the conflict. Journalist and maritime historian Lincoln Colcord argued, 'We should not have taken sides.' In fact, he accused the America First Committee of 'trying to carry water on both shoulders,' for it was endorsing aid to Britain in principle when strict neutrality was called for. Similarly Lawrence Dennis, in an obvious reference to the sentiment embodied in the AFC, said that the noninterventionists should never have abandoned absolute neutrality. By endorsing 'all-aid-short-of-war,' they could only fight rearguard actions and postpone the inevitable.
"Other anti-interventionists supported the continued flow of war goods to Britain. General Wood sought to rush steel and remove bottlenecks on planes. Colonel McCormick wanted Britain to have whatever it required, though he did not think it needed anything. Charles A. Lindbergh, far more cautious, favored continuing current aid to Britain but stressed the need for negotiated peace; hence, such assistance should neither be increased nor continued indefinitely." Justus D. Doenecke, *Storm on the Horizon: The Challenge to American Intervention, 1939-1941,* pp. 170-1.
https://books.google.com/books?id=XYFTZYJTyGAC&pg=PA170
(What led me to reading Doenecke's book was a passage in Jack Ross, *The Socialist Party of America: A Complete History,* p. 411.
https://books.google.com/books?id=MnflBgAAQBAJ&pg=PA411 "Virtually no one in the anti-interventionist camp was indifferent to the plight of Britain; even Robert Wood of the America First Committee endorsed Herbert Hoover's argument for aid short of direct military aid." He gives Doenecke's book as a reference. "Virtually no one" is an exaggeration, but it is true that many so-called isolationists did favor *some* kind of aid to Britain, as Doenecke's book makes clear.)