The US has pretty much always made Social Progress in bursts. We do a whole bunch at once then do nothing for a time while things settle in. Eventually pressure starts to build as we recognize more injustices and when it builds far enough there's another burst of Social Progress.
We're currently headed into another burst but its been delayed by the sheer numbers of old people who are clinging to the levers of power until the Grim Reaper pries them off. This is entirely unique in the history of this country because prior to the 1950s or so people simply didn't live or stay healthy long enough for this problem to manifest.
Well Abraham Lincoln did get a letter from Karl Marx congratulating him on a winning second term and how the civil war's fight against slavery was a huge positive direction for workers all across the world. And Franklin Roosevelt despite blemishes like the internment of Japanese American citizens did a lot for protections for the working class.
Hey now dont ya dare discount Theodore Roosevelt, he laid the groundwork for Franklin Roosevelt in many ways. He also established the national parks, pushed early environmental legislation, and broke up corporations with his trust busting efforts. And thats not even getting into his conservatorship and diplomatic efforts. Really most of his bad spots are the definition of part of his era, IE the whole white mans burden shtick. But even then he generally respected the cultures he interacted with, which puts him leagues above his contemporaries with maybe some colonial commanders who actually knew the locals they were in charge of and respected them.
In the early 20th century due to growing social unrest around the world and socialist populism. The Democratic Party did for at least one presidency lean significantly further to the center than it does today. However that particular president failed to hold fascists accountable and despite making huge short-term gains. Long-term lost the game.