109 retired generals is far more than you can regularly expect on ordinarily political matters. For context, nominations for secretary of defense generally elicit opinions from retired generals. James Mattis, who quite possibly is the most popular military general for several decades, only ever received a couple dozen public expressions of support for confirmation as secretary of defense. The fact that 109 generals publicly opposed any confirmation of a Secretary of Anything, let alone a director level position, and did so in a unanimous letter, is absolutely massive.
Active duty generals generally do not comment on political matters. Once they have left military service it's much easier for them to give a public opinion about politics without creating a conflict of interest.
109 generals sounds like a large number. It's a compelling metric!
But, I don't really know how many generals (and admirals) there really are in the military. I just know that the US military is kinda huge, so there's got to be a lot of them. I mean, the Pentagon alone is a massive building (the largest office in the world!) that I imagine being full of generals.
And then, I see in the letter that all of the signees are retired, which expands the total number of generals (and admirals) alive significantly.
I guess, I'm trying to ask a question about metrics, because I face this constantly. The absolute metric (>100 generals!) looks very strong, but the relative metric (nn% of all living generals and admirals active and retired) would possibly be underwhelming. It's no small feat to get a person with a real voice to sign a public letter like that so, the absolute number is big, but if the cause were of broad interest the relative number would be significant too....
On a minor bit of research I see there can only be 231 flag officers active at any time. I don't know how many are retired, but that does indicate the absolute number is a significant relative number. I still just struggle with the right way to report and digest metrics like this.