<<The size of the Supreme Court has been changed many times in the past. >>
Certainly not in the recent past, possibly not even in living memory. The last ATTEMPT to change it was FDR's and I don't know when the last actual change was made.
Here is a little serendipity. In trying to research that question I found this vindication of my original suggestion (one might better call it a confirmation of my fear) that someone on the left has already thought this one up.
http://velvelonnationalaffairs.blogspot.com/2007/08/re-increasing-size-of-supreme-court.htmlI'm going to post it in a separate thread, because I think it goes beyond the initial scope of this one and deserves discussion on its own merits, but I wanted to answer your post. You are, I'm certain, quite correct that it has not been tried since FDR. I think the increased exposure of the mass media has made major changes of this type far less likely. The great thing about a free press is it helps keep politicians honest. Imagine the controversy that would erupt if this issue comes up. But if the Dems can shut down the right-wing talk shows using the "fairness" doctrine and keep their message on the left-leaning mainstream media, they might very well decide that they can invest in an increased SCOTUS size and deal with the political consequences, secure in the knowledge that the court leans their way and all will right itself with time.