“...If you wouldn’t be a Republican in 1861 I don’t know why you would be one now...”
Because I would rather be part of a Republic rather than an empire. As H.L. Mencken said when discussing the eloquence of the Gettysburg Address but noting that self-determination is what the South fought for, he stated that the states went into the war as sovereign states and came out as districts and “what they lost they never got back”.
States where never sovereign after adoption of the constitution. Under Article VI clause 2, the constitution became the supreme law of the land.