The list of previous months content.

How's how I search.

https://www.democraticunderground.com/?com=archives&date=2023x12

for one example

a keyword and/or the author's name in your search. You'll need to specify the date range, and since GD is so active, searching for a commonly used name or keyword (or threads from a DUer who posts a lot in GD) will mean you'll often hit the limit of 24O results before the complete date range (even a range like a month) is searched, so you'll have to edit the search to see more results.