Just Pearl Harbor? How about the depths of the worst of the depression 1932-1940 (which he handled miserably)
FDR has always made my list of worst 3 POTUS in US history.
FDR is responsible for three things: leading the country during The Great Depression, being in charge during WWII, and setting up the modern welfare state.
The latter is the chief reason Democrats regard him as a hero.
His actions to combat the depression were disastrous.
He did a reasonably good job letting the military run the war without too much interference and helping Britain get arms to fight Hitler.
But his actions grabbing power and forcing business and industry to do his bidding prolonged the depression by at least five years. (Herbert Hoover gets a lot of blame as well. The Smoot-Hawley Tariff was passed during his admin.)
And although he, Roosevelt, expressed misgivings about future citizens taking advantage of welfare, he's the one who put the foundation in place.