Most of what passes for Civil War history today simply repeats story lines developed in the Times 1861-1865.
So Morgan gave up his party chairmanship in 1864 and picked it up again in 1872. That could have been due to the weakening of the Weed machine :
In 1862, Thurlow Weed tried to secure the New York State [party] gubernatorial nomination for [General John] Dix. He [Dix] lost the Union nomination to General James Wadsworth, whose views on slavery and the war were more radical.
("Union" here refers to a Republican front organization, a fusion party designed to split Democratic voters.)
Will report back on this Raymond-for-Morgan business.