The PhD electorate are "postgraduates" after you cut out all the MDs, JDs, MBAs and other non-academic degrees. There's also going to be a heavy bias towards folks working in academia/research among PhDs that is less pronounced in the larger "postgraduate" demographic.
Men still outnumber women in PhD graduates. In the STEM fields there's also going to be a heavy bias toward Asian immigrants. All in all, I'd say that PhDs were probably Republican leaning up until the 1960s but have since become a reliably Democratic group. The admission of MDs/JDs/MBAs would move this group considerably to the right, however.
Probably not on the bolded. There are far more JDs (about 1.3 million) than MDs (about 600,000) and I believe than MBAs (but couldn't find data on number of holders), and JDs are a very strongly Democratic group (as I recall, polling by the ABA in 2016 suggested JD holders were voting more than 80% for Clinton - can't find the source right now). I do agree that MDs are about evenly split, and MBAs should be fairly Republican.
Donation information is easier to find; lawyers and law firms donated $34.6 million to Hillary Clinton in 2016 and just $942,000 to Trump (plus a bunch more to other Republican primary candidates, but still way less than the Clinton total in aggregate).
https://news.bloomberglaw.com/business-and-practice/how-much-money-did-lawyers-contribute-to-the-presidential-election/
This all aligns with my anecdotal experience of working as a lawyer, too, which is that Republican lawyers, even at the highest income levels ($1m+ annually), are a relatively small minority.
I guess it depends on whether or not PhDs are more or less than 80% Democratic. I'd wager they're >80%, so the addition of JDs/MDs/MBAs would make the total "postgraduate" demographic more Republican than it would be otherwise. The ABA number is interesting, but sounds pretty lopsided to me (so I'd love to see the original source and methodology.) The donations point towards Democrats being heavily,
heavily favored among attorneys, but I imagine the law firms/attorneys organized to make political contributions skew towards big time trial lawyers and not the more numerous "local" law firms.
