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Thanks to @PostEverything and @cshea4 for giving @proffontana and me some space to talk about judicial nominations. This piece includes some stats. More in this 
https://twitter.com/PostOpinions/status/1361749093580763137
https://twitter.com/PostOpinions/status/1361749093580763137
Trump's judges were really young. At nomination, his circuit judges were 47, on average, which is the youngest since at least Teddy Roosevelt, at the beginning of the 20th century. (And I don't know that anyone has compiled stats from the 19th.) /2
Check this out:
Of the youngest 25 federal circuit judges nominated since Reagan, all of them were nominated by Republican presidents. /4
And here are the youngest 50 since Reagan. 46 of them appointed by Republican presidents. /5
Of the youngest 100, 76 appointed by Republican presidents. Here's 51-100. /6
Here's one way to think about the age gap: take the average age difference between Trump and Obama circuit judges = 5 years; multiply by # of judges (Trump had 54); and multiply by average # of cases decided per judge each year ... /7
FJC says federal circuit judges averaged 427 "terminations on the merits" in 2020 ( https://www.uscourts.gov/sites/default/files/data_tables/fcms_na_appprofile0930.2020.pdf). So that's 5 (average age gap) x 54 (# of judges) x 427 (average cases per judge per year) = 115,290 cases. Assuming age at retirement is a wash (which is plausible) ... /8
and other things equal, that's roughly how many more cases Trump's circuit judges will decide as compared with Obama's. You can run more conservative estimates with your own numbers. But note that the age gap extends beyond Trump and Obama to other Dem/GOP presidencies. /9
So those also have to be factored in. Even without intangibles (building jurisprudence, leadership, networks, etc.), the age gap has effects for who decides cases. (For modeling of age-based ideological shift in the courts, see Katz and Spitzer, https://arizonastatelawjournal.org/wp-content/uploads/2017/11/Katz_Final.pdf.) /10
Last point: age is a proxy for other factors. GOP presidents tend to select nationally for talent, ideological commitment, youth. Dems tend to select for experience, support of state/local bar, and diversity. The Dem model has important virtues, but ... /11
it also has real costs. It's not obvious why there has to be any tradeoff between diversity and youth. And after that, Dems have strong reasons to reconsider the historical patronage model, which has traditionally worked against advancing younger and more diverse nominees. /end.
