There are at least two things wrong with this claim. First, it couldn’t possibly be true unless it were the case that no credentialed historian is a Trump supporter; even one or two (and I bet there are a lot more than that) would spoil the broth. Second, and more important, the profession of history shouldn’t be making political pronouncements of any kind. Its competence lies elsewhere, in the discipline-specific acts I identified above.

Were an academic organization to declare a political position, it would at that moment cease to be an academic organization and would have turned itself — as the Historians Against Trump turn themselves — into a political organization whose arguments must make their way without the supposed endorsement and enhancement of an academic pedigree. Its members would be political actors who share the accidental feature of having advanced degrees. But it’s not the degrees, which are finally inessential, but the strength or weakness of the arguments that will tell in the end.

If academics are wrong to insert themselves into the political process under the banner of academic expertise, is Ruth Bader Ginsburg wrong when she makes unflattering remarks about Mr. Trump at a conference and in an interview? Maybe so (indeed, she herself has expressed regret for the comments), but she has not committed the same transgression as the historians. Justice Ginsburg was speaking off the cuff, offering her opinion on a matter currently in the news, as any citizen has a right to do. She did not cite or trade on the trappings of her office; she did not proclaim from the bench.

The Historians Against Trump are proclaiming from the bench, not a literal bench, but the bench of their faculty offices and university positions. They are saying, here is our view of the election and you should pay particular attention to it because we are academics; indeed in speaking out, we are doing our academic job. Justice Ginsburg is saying, here’s what I think about Mr. Trump; take it for what it’s worth. For the historians, their credentials are the whole point; for Justice Ginsburg they are beside the point.

Perhaps Justice Ginsburg should have been more reticent in order to avoid even the appearance of impropriety (the suspicion will be that her partisan views will spill over into her judicial performance). But whatever the possible inappropriateness of what she said, she did not say it as a Supreme Court justice; she did not invest her remarks with that authority. The Historians Against Trump invest their remarks with the authority of their academic credentials, and by doing so compromise those credentials to the point of no longer having a legitimate title to them, at least when they write and publish their letter.