Just to address this point, here's a photo of Roosevelt:

And here's a few political cartoons to show how he was physically portrayed at the time of his presidency:

The film portrays the FDR stereotypical look pretty well in that regard.

Except it wasn't.The 1944 US presidential election (which this film was made for) was between Roosevelt and Dewey. Truman was FDR's vice-president at the time and took the helm of the country following the latter's death in 1945. Truman did face off against Dewey in the 1948 election, which I believe is what you're thinking about here.