As I have noted many times before, George Washington was not a "strict Deist" like Thomas Paine and to the extent that some folks hold this misconception, Peter A. Lillback, the Novaks and other scholars who dispel this notion do relevant work. The problem, though, is many of them then argue Washington was a "Christian" (as though there were only two boxes "Christian" or "Deist"), but Washington's belief in orthodox Trinitarian Christianity simply cannot be gleaned from the historical record.
While it is quite easy to construct a strict Deist strawman and offer an avalanche of facts on Washington to knock it down, little if anything I have seen from Lillback or the Novaks demonstrates Washington believed any differently than Jefferson, Adams, Franklin, and Madison. If we call their belief system "theistic rationalism," this is not such an easy strawman to knock down. Lillback's book thus is full of non-sequiturs, offering many facts about Washington suggesting they demonstrate he was an orthodox Christian, when they do not. For instance, there is a chapter on Washington's prayers where they deal with Washington's "reciprocal prayers." As Lillback points out, "[t]his is a gracious custom that could be construed as a mere civility." He should have stopped there. But he goes on:
But in some instances, this cannot be offered as the explanation. That is because some of the prayers are so explicitly Christian and biblical, that to affirm a reciprocal prayer would be to confess a Christian faith. If Washington intended to be the honest, candid person that he claimed to be, and yet also was the Deist that so many have claimed him to be, he could not have offered a reciprocal prayer in such instances. Yet, that is exactly what Washington did on various occasions. p. 362-63
Lillback then quotes some of the original letters to whose prayers Washington reciprocated. For instance, one from the Reformed Protestant Dutch Church in Kingston which prayed, for Washington, an orthodox Christian prayer, talking about entering Heaven through the "Blood of the Lamb." Lillback writes, "[s]urely Washington, if he were a Deist, could not reciprocate such a prayer. But he did." p. 364. But notice, when Washington reciprocated, he repeats none of the orthodox language, just stated that his "wishes are reciprocal."
Convinced that our Religious Liberties were as essential as our Civil, my endeavours have never been wanting to encourage and promote the one, while I have been contending for the other; and I am highly flattered by finding that my efforts have met the approbation of so respectable a body.
In return for your kind concern for my temporal and eternal happiness, permit me to assure you that my wishes are reciprocal; and that you may be enabled to hand down your Religion pure and undefiled to a Posterity worthy of their Ancesters is the fervent prayer of Genre. Yrs. &c. 5
Now let us turn to Jefferson doing the same thing. In fact, let us turn to what is arguably Jefferson's most famous correspondence on church/state matters -- his letter to the Danbury Baptists. While many people are aware of the letter Jefferson wrote to them, few know of the letter they wrote to him, to which he responded. Here it is. And let me excerpt part of it: "And may the Lord preserve you safe from every evil and bring you at last to his heavenly kingdom through Jesus Christ our Glorious Mediator." This is an unequivocal statement of orthodoxy from a Church -- the Baptists -- which was unquestionably orthodox in its doctrines.
To which Jefferson responded with his famous letter stating the First Amendment instituted "a wall of separation between Church & State." But few people notice the very bottom of the letter where Jefferson reciprocated their prayer.
I reciprocate your kind prayers for the protection & blessing of the common father and creator of man, and tender you for yourselves & your religious association, assurances of my high respect & esteem.
In short, Jefferson here does exactly what Washington did with his reciprocal prayer to Reformed Protestant Dutch Church. And we know from reading his private letters, Jefferson rejected almost all of the tenets of orthodox Christianity. It no more follows that Washington's reciprocation signified a belief in the orthodoxy of the original letter writers than Jefferson's reciprocation did.
As I noted above, Lillback had the common sense explanation for Washington's reciprocal prayers, that it was "a gracious custom that could be construed as a mere civility." He should have stopped there and not delved in deep to a non-sequitur. His book is 1200 pages of this kind of argumentation.