There is ample anecdotal evidence that George Washington was capable of cursing, for instance at the Battle of Monmouth:
General Charles Scott, who later became governor of Kentucky, said it was the only time he heard Washington swear. "It was at Monmouth and on a day that would have made any man swear", Scott said. "Yes, sir, he swore that day till the leaves shook on the trees, charming, delightful! Never have I enjoyed such swearing before or since. Sir, on that memorable day, he swore like an angel from heaven."
If one checks the historical record, one will find several such "isolated" incidents, as attested to by various Washington contemporaries.
Sounds like a liberal “witness” to me.