CA has only elected democratic (vaguely to the left of the median Democrat, if fairly rank-and-file) senators since 1992. As long as she didn’t leave it to chance and die during her term (…) while she coincided with the honestly fairly moderate-but-still-republican Gov Schwarzenegger, she could have had a hand in picking her replacement.
As others (including myself) have noted, any Democrat-led SCOTUS nomination or major piece of Dem legislation would have passed more-or-less the same. I’d be curious if there was some analysis of where a particular Dem Senator from CA was a “swing vote”. Meanwhile now we’re in a vacancy and her missing vote definitely matters (again, thankfully likely with less impact than RBG’s).
If you’re “entirely serious” in the literal sense, just to be super clear the answer to “why can’t the Democrats run an intellectual Canadian?” is that a Canadian is disqualified from the office of the President in the Constitution. Unfortunately, they didn’t think to prohibit megalomaniac felons. That’s apparently on us. :(