"As to your concern for the conversion of infidels, I look upon it as the cant of a philosophical crusader, and am sorry I cannot coincide with you in your projected conciliation of the rational truths of philosophy, with the mysterious truths of Christianity. I am apprehensive that it is impossible, without endangering the cause of both, to bring them into too close a contact....It is a moot point with me, whether the really thinking and intelligent philosophers, whom Dr.Priestley wishes to convert, are greater infidels in their present state of unbelief, than they would be, if converted by him into rational Christians,..."
This is notable because the heterodoxy in which Jefferson, J. Adams, Franklin and probably others believed in (i.e., Joseph Priestley, Richard Price influenced theology) didn't present itself as "deism" or "infidelity" but "rational Christianity." But to the "orthodox," this "unitarian" "rational Christianity" was not much different than the "infidelity" of strict deism. Still it enabled Jefferson, J. Adams and Franklin to couch their political-theological plans under the auspices of "Christianity." Their republican project wouldn't have succeeded if done otherwise.
Priestley later explains (scroll down a few pages) what "rational Christianity" is all about:
If, for example, bread and wine, philosophically, i.e., strictly and justly considered, cannot be flesh and blood, the popish doctrine of transubstantiation cannot be true. So also if one cannot be three, or three, one, mathematically considered, neither can the Athanasian doctrine of the Trinity be true. It certainly, therefore, behoves every rational christian to prove the consistency of the articles of his faith with true philosophy and the nature of things.
This also, to me sheds light on Leo Strauss' argument that, however much they may agree on some or many things, reason and revelation ultimately boil down to inconsistent teachings.