You’re right, it was Dewey in ‘44. However, early in the primaries Willkie raised the issue of FDR’s foreknowledge early in his campaign among GOP leaders. He planned to make the issue a major thrust of his primary campaign. In the interest of national security, he abandoned the issue.
Too bad Taft didn’t get the info. Even in 1940, Willkie was pretty much an FDR shill. He was the John McCain of the 1940s.