It’s difficult to establish how much the public knew about FDR’s disability, but there was no great cover-up in the way it is often portrayed. The press did not talk about this, pictures of him in a wheel chair weren’t published, but many people saw him in a wheelchair, being carried by his assistant, and even while wearing leg braces he couldn’t walk without assistance. However, I have no doubt that JFK, a political insider, was aware of the extent of his disability.
In these times it may be difficult to believe that a sense of decency stopped public discussion of this subject, but polio was an epidemic and people were well aware of the impact of this disease on the human body. FDR campaigned on the concept that he had beaten polio, but many people would have thought at best that he could walk with leg braces and the aid of a cane or crutches. His condition was much worse than that, but people probably didn’t care, they knew about the results of polio on the human body, and simply returning to a public life and maintaining his career as a politician was inspiring enough for people to assume he had ‘beaten polio’.
The problem in all such discussions as these is defining what “people” or “the public” knew. Do we mean the people who saw Roosevelt with their own eyes or the 44 million who voted in the 1936 election? Most of the time we seem to mean the latter, but no evidence is ever given except anecdotes and must-have-beens and pointing to insiders.
Except that we have an actual statement from his secretary that he absolutely did *not *know until he was admitted into an insiders’ gathering. I’d say that is hugely powerful evidence.
The best evidence I can find from reading about Roosevelt is that the general voting public did believe he had beaten polio to the extent that he could walk and therefore was not a “cripple” as it was thought of at the time. The supporting evidence comes from the multitude of accounts of the lengths he went to in continuing to fool the public throughout his presidency. His public appearances were carefully contrived to never put him into a position where his level of needed assistance was visible. He drove in motorcades or appeared at the end of a train. He made speeches in closed halls where he only needed to walk to a podium or a center table. He was photographed sitting behind his desk or seated while giving a fireside chat. It’s certain that the press corps got backstage glimpses of him, but as you say these were virtually never transmitted to the public. (One or two got through courtesy of his enemies.) There was gossip, but most of it was at the factual level of Obama being a Muslim; it was a way to attack him rather than a knowledgeable statement.
I don’t see any way of proving the level of knowledge at this distance. People are not likely to want to admit being fooled and so any retrospective surveys are tainted by the later revelations. Nor could you possibly have asked that question while he was alive. For me, the fact of his extensive, painful, and continuing efforts to hide his inability to walk is sufficient to make the case that the general public did not know. Some small fraction of them did, but I can’t even guess at the percentage.
How many of them would care if they had known is another unanswerable question. Roosevelt clearly thought they would or he wouldn’t have put so much effort into deceiving them. He won by such overwhelming margins that it’s hard to believe enough would care to turn their votes against him after 1932 or even in 1932. But we just don’t know.
There were only two (IIRC) such pictures taken, and you are correct, they were not published. Roosevelt never appeared in public in a wheelchair, but used one in the White House where staff clearly saw it.
Roosevelt appeared in public driving or riding in his hand-controlled Packard. He’d be riding and not getting out in crowds of pedestrians. Everyone knew why. Eleanor Roosevelt did a look of touring and was called his “eyes and ears”. Everyone knew he had polio. What took with the public was that FDR didn’t let polio stop him from doing anything. It wasn’t the worst case where someone died or ended up in an iron lung, but the car thing and the “hip hiking” walks were shows of carrying on. Incidentally, the “hip hiking” walk was practiced a lot, and if you’ve seen anyone else do it, FDR made it far closer to natural. And he smiled while doing it. The leg braces were quite painful.