Franklin Roosevelt, far from championing Social Security legislation passed by Congress, actually vetoed the bill the Republican Congress passed as a boondoggle. (See FDR Vetoes Social Security Legislation; Republican Congress Overrides, from 1943.)
Mark Hodak explained on his blog: "Roosevelt, of course, promoted and signed into law the original Social Security Act of 1935. But that law set up a forced savings/redistribution program for limited portion of the population. It used the contributions from the participants to set up reserves, and it paid beneficiaries from those reserves. The plan was more or less self-contained. In 1943, President Roosevelt vetoed legislation that would turn Social Security from the forced savings/redistribution program it was set up to be into the pay-as-you-go program that, once his veto was overriden, we know today.
The 1943 debate on this law centered on governance. For Roosevelt, good governance meant continuing the Social Security program as it was originally envisioned–actuarially self-financing. To Arthur Vandenberg and other Republicans, it was clear that Congress was simply using the “reserve fund” as a cover to squander money on pet projects. In their minds, shutting down the “reserve” was just a way of restoring fiscal discipline.
More details here: Would Roosevelt Recognize Today's Social Security? by Robert Samuelson.