Underwood was a straight up leftist. Or were you suggesting Bryan was conservative? More so than William Jennings maybe, but still on the left side compared to the likes of McAdoo or Smith or...Davis.
Underwood was not a straight-up leftist; he was a segregationist who opposed the Klan because he believed the Klan stymied him in 1920 in supporting William Gibbs McAdoo. Underwood feuded with Woodrow Wilson in Wilson's second term, leading Wilson to say about him at one point, "If Underwood is a Democrat, then I am a Republican!". His "liberalism" is overstated due to his opposition to the Klan. In contrast, Sen. Theodore Bilbo (D-MS) was perhaps the most vile racist ever to serve in the Senate, but he was a New Dealer DOWN THE LINE! You cannot gauge the "liberalism" of Southern Democrats solely by their personal moderation on race when it comes to pols of Underwood's age.
What is most interesting to me is what history would be like had Hiram Johnson become President. Would the GOP have been the party of Civil Rights in the long run? Would the monied interests become Democrats? Would we be as internationalist today as we have become? Had this scenario taken place, the Civil Rights movement would have played out much differently than it did, with a different set of folks being its heroes.