You have just provided us with some more evidence of it.
“Some years ago, I realized the 1860 Republicans were the liberals.”
Some of them were radicals of the Left, way beyond liberal. The Radical Republicans were a very powerful group within the early GOP right through the late 1870s.
Some of that was due to the influence of ex-patriate ‘48er German revolutionaries who helped found the party. Literal pals of Karl Marx who had fled to America after bungling their European takeover.
Some was from Northern Puritan culture as it discarded Christianity in favor of “imminentizing the eschaton” via politics, a habit that characterizes the Left even today.
You can find early American Communists lamenting that the Republican Party was “the one that got away!” after an illustrious beginning. They remembered the early history after everyone else had forgotten it.
The Communist side in the Spanish Civil War called itself the Republicans. The American volunteers called themselves The Lincoln Batallion and the John Brown Brigade. Some of that wasn’t just coincidence, that’s the portion of American history that they identified with.