well for starters johnson’s national union probably gets off the ground as opposed to it simply falling due to it basically being a democratic party but without the machine power
now this does bring up some interesting questions - particularly around a potential impeachment + removal of johnson with a slightly more radical republican congress, which honestly probably does happen, and a more radical congress also almost 100% guarantees an annexation of the DR.
not only that but the legal precedent used to ban the democrats implies a much harsher reconstruction, so i’m assuming that many prominent leaders of the CSA are either strung up or left to rot
now, let’s talk about the ramifications of this on the republicans. first and foremost without a democratic party and presumably without a klan, the US is a dominant party state until at least the 1890s. that begs the question: how do republicans evolve? it’s pretty plausible that they could end up being a strange mix of vengeful christians who hate immigration mixed with support for civil rights and breaking down the planter class. this will come both as a result of the republicans know-nothing roots and the fact that they’ll at least be cracking some skulls in tammany, let alone the other ethnic white machines. there was also a general sentiment, expressed most famously by sherman that the us had to somehow bring gods wrath down on the south, which may happen.
this strain of what we’ll call “christian democracy” will likely have many non-democratic party opponents, specifically classical liberals, like charles adams, who were major supporters/members of the liberal republican party in 72 and of the gold democrats in 96, which means yes, you can get the christian democratic/libertarian party system we’ve all salivated over.
there’s also the possibility of a radical left wing opposition party, based in the leftist aspects of the populists/greenbacks/agrarians, empowered blacks, immigrant class, and some other white poor organizations, standing in opposition to the republicans. the only issue is keeping these groups united throughout their differences and without the bryanite christianity that will certainly exist in the republican party.
either way a major jumping point for either group could be a growth in american imperialism, which could definitely be utilized by the left/classical liberals
this is a very interesting idea though and i’m a big fan as always rosa.