I don't know of anytime when the Dems had a filibuster proof majority. You must be thinking a long time ago. Probably back when you had Southern Democrats, Conservative Democrats. I think the last from the South Might have been Alabama's Howell Heflin. These Southerners from way back were likely anti-choice. Al Gore had been anti-choice.
Today this portion of the electorate is voting for Republicans. The country did not move to the Right, its just that some voters of the Right switched parties.
Anyway, Harris is not making up the language of "settled law" up. It was applied by the court to Brown V Board. And in the early 90's, responding to the Casey challenge when they upheld Roe, and responding to the insult to the court of the moron Clarence Thomas being seated, they issued their statement that Roe v Wade was settled law.
Doesn't mean that that it could not possibly ever be changed, but it meant that they don't think it should be changed, and that someone like Clarence Thomas should not be on the court.
O'Connor being part of this was significant because she is of an anti-Choice leaning and Roman Catholic, and she did not really like the Trimesters concept in Roe. But still, she did not think Roe should be changed, and really, someone who says they had never thought about it and who did not voice support for Roe, as they do for Brown v Board, should not be allowed on the court.
So Harris is simply repeating what is taught, up until now, in our finest law schools.
SJG