Our English language sits on shifting sands and researching them, at least for language mavens, is fascinating. For instance, did you know that the noun “Democrat” wasn’t affiliated with the adjective “liberal” until the 1930s? Before that, it is most often seen with the words “Southern,” “good,” and “little” (which is apparently not a pejorative use—”Little Democrat” was the name of a ship that spawned a diplomatic dispute between the US and France).
There have also been shifts in how “Republican” has been used. From 1910 to 1950, “progressive Republican” was somewhat common, before being eclipsed in use by collocates such as “conservative” or “moderate Republican.”
Anyhow, political labels aside, the National Endowment for the Humanities introduces us to Brigham Young University’s Corpus of Historical American English. But be prepared. If you like this kind of thing, free access to the Corpus means a lot of lost time before you know it.