Why was FDR (a pre-1964 dem. (modern day repub.), able to serve more than 2 terms?

He's the only one

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George Washington, our first president, declined to run after two terms. He declared that two terms were enough for any president. So, the 22nd Amendment took effect in 1951; and the office is limited to a maximum of two full terms, or eight years

It was always a "law", just, it was never an "enforceable law", until 1951
Why was FDR (a pre-1964 dem. (modern day repub.), able to serve more than 2 terms?
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