But now we are faced with yet another question. If it was Robert Walpole who said " Our American cousin has run off with a Presbyterian parson." then we can deduce that Walpole was not referring to the American revolution, because Robert Walpole died some 30 years before the revolution occurred.(1745)
Actually, looking back on the development of my article, I'm inclined to lay the blame at the feet of Loraine Boettner (sorry, Mr. Boettner).
Historians Donehoo, Stohlman, and Wills all attribute the quotation to Horace Walpole, on the news of the Declaration (of which Witherspoon was a Signatory) in 1776; Donehoo in particular does record Walpole as adressing the English Parliament (Horace was a "gothic novelist", but he also was in fact an active Member of the House of Commons from 1741 to 1768, although by 1776 he would have been offering Parliament his opinion as a Private Citizen, not speaking in any official capacity).
It is not until we get to Boettner's "Calvinism in America" that Mr. Boettner, either as a simple oversight (if we are charitable) or perhaps in an attempt to "juice up" the Authority of the quotation a bit, makes Horace out to be the Prime Minister -- thus confusing him with his illustrious father.
Unfortunately, Mr. Boettner's confusilation of Horace's position with that of his father Robert has been repeated by numerous writers ever since -- including, embarassingly, me.
Sorry for the confusion... a case of GIGO.
Best, OP