Question - what is the essence of the Republican Progressivists and Democrats contradictions, and how do they differ from the OTL counterparts?
The Democrats are social democrats, similar to OTL European social democratic parties (albeit more populist), or like progressive Dems in the OTL United States. They also allied and merged with some state-level Socialist Parties, such as in Wisconsin

The Republican-Progressives, contrary to their name, aren't very progressive by TTL's standards, instead they're similar to OTL European liberal-conservative parties, or like OTL John Kasich. They do have a slight civic nationalist bent though

The Republican-Progressives used to have a progressive "Roosevelt wing", but they mostly emigrated to the Democratic Party in the 60s and 70s

Since the 2016 election Adam Sharp has been much more populist than the majority of the Republican-Progressive Party, but he's not quite Trump. Before that he was just a normal Republican-Progressive though
How is the US politcal map? Does the solid south still exist? Is the west still Repiblican?
The political map is similar to OTL with some differences. Missouri and Arkansas are swing states, as are Colorado, New Hampshire, and Maryland. Louisiana leans Dem thanks to popular Democratic Presidents Huey Long and Tommy Mahfouz both hailing from Louisiana, and North Carolina usually goes Dem. Virginia leans Republican-Progressive but sometimes flips to the Dems. The rest of the south goes Republican-Progressive, as does the interior west, although the west coast goes Dem. Additionally, Baja California and Puerto Rico, the two "Hispanic states", both lean heavily Dem

Although in general states are more swingy ITTL. The only truly "solid states" are Baja California, Puerto Rico, Alabama, Mississippi, and South Carolina, of which the first 2 always go Dem and the last 3 always go Republican-Progressive
Here are the infoboxes for the 2 major parties in TTL's United States

Democratic Party (USA).PNG
Republican-Progressive Party (USA).png
Really liking this TL! Are there any major third parties in this US?
Yes, I haven't developed them much yet but there's a Green Party, a Libertarian Party parallel under a different name, a Baja California regionalist party, and some others

Interesting political system here! Can you do a Presidential Election next?
I might, yeah, but I've been getting somewhat burned out lately so I'm not sure how fast it'll come
Nice! How did the democrats get North Carolina and louisiana? Do they have larger black populations ITTL?
I'm not sure about racial demographics, but the political demographics are certainly shifted. I haven't really decided on NC but Louisiana is because of two popular Dem presidents of the 20th century (Huey Long and Tommy Mahfouz) hailing from Louisiana
2016 US presidential tickets
I've had these sitting around for a few days but never bothered to post them until now. Here's the presidential tickets from the 2016 American election. I plan on doing the primaries for both parties soon as well

2016 Republican-Progressive ticket.PNG
2016 Democratic ticket.png
1912 United States presidential election (initial POD)
Finally did the POD, complete with 5 candidates winning states and a really low turnout due to disillusioned voters after the Dems fractured. They fractured because Wilson dropped out of the race after a heart attack, they nominated Champ Clark, and WJB decided to run as a Populist in protest. I know the exact results are probably not the most realistic, but a few alien space bats here and there can't hurt too much

1912 US election.png
1916 US election
Another US election, this time with the Republicans cross-endorsing Teddy because he was a semi-popular incumbent. He didn't get a landslide victory though because people were wary of him running for a third full term

1916 US election.PNG
How did Debs get so much support in 1912 and 1916?
Started out with disillusionment after both parties fractured, then his support just didn't go away until later

Edit: but OOC it's because of the semi-chaotic politics of the HOI4 Reich mods, the fact that I like Debs, and that I like third parties having more success