But he couldn't figure out what to call them.
Rev. Samuel Miller was a professor at Princeton and corresponded with and about America's Founding Presidents. He was an orthodox Calvinist (in fact one of the few notable ones that supported Jefferson).
In this book written in 1821, Miller denies Unitarians the title "Christian." The Unitarians, who thought of themselves as "Christians" so responded:
... Dr. Miller professes to submit his Reply to the "Christian public;" and it is certainly very unreasonable in him to complain, that we should decline our agency in forcing it upon a class of persons, whom he holds not to be Christians.
It is no wonder, that Dr. Miller, after denying to us the name of Christians, should be puzzled in deciding what to call us. "There is a real difficulty," he says, "in giving a convenient name to these persons as a general body." We beg leave to tell him, that this is a difficulty of his own making. We have never asked him to be at the trouble of giving us a name. We are perfectly satisfied with the one, by which we have always chosen to call ourselves; and really we cannot see, why he, or any one else, should think it so great a tax upon his courtesy and condescension to give us the "distinctive title," which he says, and which we allow, we have "assumed." The difficulty of giving us a name, he informs us, arises from the circumstance of our "differing so materially among ourselves." Does he mean by this, that Trinitarians do not differ equally as much? The truth is, the differences among them are vastly greater, than among Unitarians, not only in regard to the distinguishing doctrine of their faith, but all the leading doctrines of Christianity. And yet, we have never found any "difficulty" in giving them a name, because we are entirely willing they should have the one, which they have "assumed." Whether it be, or be not, a title, which designates their opinions, is no concern of ours. It is enough that they choose to adopt it. If they misname themselves, it is an affair of their own. We do not see in what respect we have any ground of complaint, or any right to interfere.