"But the principal argument for reposing the power of pardoning in this case [i.e., that of treason] in the chief magistrate is this—In seasons of insurrection or rebellion, there are often critical moments, when a well timed offer of pardon to the insurgents or rebels may restore the tranquility of the commonwealth; and which, if suffered to pass unimproved, it may never be possible afterwards to recall."
Federalist No. 74, ¶ 4.
It's rather difficult to read this passage as not presupposing the validity of pre-conviction pardons. Not impossible, of course; but difficult.
Yes, yes; a newspaper editorial is a newspaper editorial, even when Alexander Hamilton is the author, and more than 200 years have passed since its publication date. But at least it's
something. Any evidence favoring the opposite position is welcome.