I've argued or observed on these pages that the prevailing political theology of the American Founding was theologically unitarian (or at least, a lot of leading light Founding Fathers and their theological influences seemed to sympathize with it).
One argument goes, since the Bible clearly teaches the doctrine of the Trinity, an endorsement of unitarianism is necessarily rationalistic, or something that relies on man's reason as opposed to what the Bible really says.
That may be valid. Others assert the pages of the Bible itself, properly understood and interpreted teach theological unitarianism.
The distinguished theologian of classical theism -- Samuel Clarke -- was a theological unitarian of some sort (how Clarke exactly understood the doctrine of the Trinity is a subject for another post; at the very least he didn't hold to what the classic ecumenical creeds taught on the Trinity).
Clarke was a rationalist. But was it his "reason" or the pages of the Bible itself that led him to his views on the Trinity? That's a question I'll leave unanswered for the moment.
Dale Tuggy, a Professor of Philosophy at SUNY Fredonia, was influenced directly by Samuel Clarke's arguments to reject the classic doctrine of the Trinity, for something that might be more aptly called "biblical unitarianism." Or perhaps Dr. Tuggy, after Rev. Clarke is coming to unitarianism because his own reason so concluded.
Anyway here is the link to the above mentioned title.