Newsom has said a replacement for Feinstein would be temporary, not one of the current candidates. I don't think it matters at all, anyone appointed would vote in lock step with their party. The way I look at all of this is Democrats want to fix the deficit by more spending, Republicans want to fix the deficit by cutting taxes. They end up doing both over time, except for fixing the deficit of course.
We still have most of the Bush tax cuts in place, and most of the Trump tax cuts in place, etc. As for spending, well, Republicans like to TALK about cutting it. Somehow.