Which of these was the worst mistake made by a U.S. President?

[Rooney]

I think Roosevelt's attempt to pack the Supreme Court was one of the worst decisions made by a modern president. I know that the Supreme Court had actively worked against the New Deal (ruling the AAA, minimum wage and the NRA to be unconstitutional) but FDR harmed his own Democratic Party in attempting to force the packing of the Supreme Court. His work to defeat Democratic senators in the 1938 primaries eroded support among the New Deal coalition and the Roosevelt Recession of 1938 helped the GOP gain 81 seats in the House of Representatives and 7 U.S. Senate seats. The GOP won 50% of the vote outside of the South for the first time since 1930.

Anger over FDR's overreach on the supreme bench could have cost the Democrats the White House in 1940 had FDR not run for reelection with the war scare. It is an amazing reversal from holding a 4 to 1 Democratic advantage in the House and a filibuster proof majority in the senate. The court packing scheme has to be one of the greatest political mistakes of the 20th Century.