Challenge: With a POD after 1900, have a US that is around as leftwing as the current US is rightwing. Instead of a center-right party and a crazy-right party, there will be a center-left party and a crazy-left party. If it makes it easier the Democrats can become a regional party in the South but the two main parties must be on the left. Bonus points if the right has as little influence as the left do today in America (though big business will be hard to put down).
Well, my TL seems to fit this challenge in spades.
It took a socialist revolution in America to do it, but the right-most party in the American political spectrum is more or less congruent with left-wing European social democracy.
My PoD was McKinley never being assassinated in 1901. With Teddy Roosevelt never becoming president, the Progressives essentially are left no other political choice but to go left and ally with Socialists in the short term.
Things get a whole lot worse before they get better though. 1 million + dead on the battlefields of World War 1 worse.