The poster isn’t exactly accurate.
The first KKK lasted from roughly 1866 to 1872. Got squashed by the feds.
The second Klan ran from 1915 to about 1926, losing pretty much all its influence by 1930.
The third KKK, as such, never existed as an organization. A whole bunch of competing organizations sprang up in the 40s and till today, but none of them ever came even close to the influence of the first, much less the second, incarnation.
I seriously doubt many KKK types for the last 40 years have been Democrats.
Even in the 20s, there were real problems fitting the KKK into the Democratic Party. Most Catholics and immigrants were Democrats, and the KKK of the 20s was more an anti-Catholic and anti-immigrant movement than an anti-black movement. (Blacks were already pretty thoroughly put “in their place” by then.) Catholics and immigrants still needed to be put there.