"The threat of adding new Justices (that would decide cases in favor of his "New Deal") was very real."
Actually, it wasn't a very real prospect, and it was not an easy reach for Roosevelt.
Those supporters in Congress? The ones who bent over backwards to pass New Deal Legislation?
They just about lost their minds when Roosevelt proposed his court packing plan. Some of the most vocal opponents to the plan were the strongest supporters of Roosevelt's New Deal programs.
Newspapers that had supported Roosevelt's New Deal also came out VERY strongly against the proposal.
"Shall the Supreme Court be turned into the personal organ of the President?...If Congress answers yes, the principle of an impartial and independent judiciary will be lost in this country." - Chicago Tribune
The court packing legislation wimpered to a final death in the Senate Judiciary Committee, where it had originally been sent by the full senate on a 70-20 vote. And, given that the chairman of the Senate Judiciary Committee at the time was VERY opposed to the court packing plan, there's virtually no chance it ever would have come out of committee in any event.
Ultimately, the court packing plan did a LOT of damage to Roosevelt. Opposition to new New Deal programs increased markedly, and virtually no New Deal legislation (certainly none of any importance) passed after 1936.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.