Quite a few interesting points about military and international politics made so far in this thread, thought I'd add a couple of notes on more domestic matters:
- One possibility is to, instead of having Benjamin Butler do entryism into the Democrats (which somehow turns them into an organizational clone of the OTL GOP), have him and other hardline right-wing Republicans form a new (Unionist?) Party, in order to avoid the damage of both the Democratic and Republican brands, as well as to make pre-GWI politics more dynamic.
- Explore the complexities of the Socialist Party more deeply, as well as its organisational differences to the OTL major parties. Either have the party split over the war (as many of its Second International sister parties, most prominently the SPD, did) and see how a split Socialist movement effects things, or don't, and explore how people like Browder, Foster, and cannon operate in the halls of an institutionalised party. Either way, explore what a significant Communist presence in US politics looks like (especially one with a native, say, De Leonist, bent), rather than just trying to ape the British party dynamic.
- Also, get rid of the absurd number of conservative OTL Democrats in the Socialist Party. Al Smith and Clarence Cannon should not be Socialists.
- Have the Rad-Libs amount to more than a wet noodle and third-wheel. I actually quite like the CSA party dynamic, especially with Craigo's additions, but i think it would be made much better by the 1920s CSA actually having a Rad-Lib administration. Tom Watson should win in 1921, then maybe bring the Whigs back for a term, then have 1933 be a mainly Rad-Lib vs Freedom contest.
- More white CS Socialists. They obviously shouldn't win anything, or even really be competitive, but they should be big enough to act as a notable spoiler for the Rad-Libs, and consistently have a small Congressional Caucus. Have Freedom constantly complain about them. I just think that'd be neat.
- As said before, have the US Socialists actually accomplish things. They should hate the filibuster (and honestly the Senate if OTL is anything to go by) and have a binding party whip anyways, so either give them some substantial policy wins, or prevent them from forming Congressional majorities until after GWII. If the latter, have the Democrats/Unionists win the Presidency more often.
- My preference would be for a Third International to emerge, and the repercussions of this to be explored. Be it in the same way as in OTL, or from a different source, there should be more attention on the global Socialist movement. Hell, I wouldn't mind a revolution in the US, even if it makes for even more parallelism, so long as its ideology isn't an expy of the USSR and is instead derived from domestic American theories and practices (I return to De Leonism as my case-in-point here).