Since court expansion is in the news, here's a quick historical note about "The Switch in Time That Saved Nine."
When FDR took office and began putting together the New Deal, he he knew that his presidency faced a Supreme Court with a solid conservative majority. In particular, it featured the "Four Horsemen," a clique of economic die-hards who almost never supported federal or state intrusion into the workplace. However, despite FDR's fears, nothing much happened during his first few years, perhaps because even the Horsemen understood the emergency posed by the Great Depression.
But in 1935 that changed. The Court sent down a flurry of decisions gutting various federal laws, the most important of which were a handful of provisions of the National Industrial Recovery Act, a cornerstone of the New Deal. FDR fumed, but NIRA was scheduled to expire soon anyway so he said little publicly. He then went on to win a landslide reelection on November 3, 1936.
Secure in this demonstration of his popularity, FDR began thinking about how to bring the Court to heel. Working in secret—which would prove to be a mistake—he eventually formulated a plan that would add a justice for every justice over 70. This would give him a reliable liberal majority.
FDR announced his plan on February 5, 1937. On March 29 the Court handed down its decision in West Coast Hotel v. Parrish, a case concerning a minimum wage law in Washington State. And guess what? One of the conservatives who often voted with the Horsemen switched to the liberal side and upheld the minimum wage. That vote change was the "switch in time," and since it doomed FDR's scheme it was said to have "saved nine."
But wait. Modern historians mostly agree that this isn't what actually happened. The Supreme Court held its conference on West Coast Hotel on December 19, 1936, nearly two months before FDR announced his court plan. That was when the vote switch happened, and since nobody knew at the time what FDR was up to, his threat to pack the court obviously had nothing to do with it.
The next big set of New Deal cases are referred to collectively as the Labor Board Cases. All of them were decided in the government's favor, but the conference for those cases was held on February 27, by which time it was pretty clear that the court packing scheme was already doomed. It's unlikely that FDR's threats influenced the vote.
And there's one more thing: the 1935 cases that so disturbed FDR were almost all unanimous. There was no reactionary minority thwarting the will of the people, it was the entire Court. Even the most liberal members agreed that certain features of the New Deal had simply gone too far.
The bottom line here is that the Court almost certainly revised its thinking all by itself. FDR's threats to its integrity had little or nothing to do with it. And a few months later one of the Horsemen retired and a couple of the others started to vote more liberally. FDR had the Court he wanted, and he would have gotten it even if he had done nothing.
POSTSCRIPT: And what's the lesson for today? I'm not sure there is one. It shows that threats didn't have any effect on the Court, but I don't think anyone believes that threats would have any effect on today's ideologues anyway. If you're going to pack the court, the only way to do it is to actually do it.
Aside from that it's just an interesting historical tidbit.