Wowie zowie. Lotta train wrecks in here, starting with the OP. Sorry I missed it.
To set a few things straight... evidence that Truman was in the Klan is sketchy at best, as has been pointed out, but the alleged association with the Democratic Party is bullshit. The kind of bullshit that resembles the toy clown thingy that you knock over and it keeps bobbing back up.
Fact is, the Klan was founded in 1865 by six Confederate war vets with no known political affiliation, and wasn't founded as a political group, or even at the time a racist group. It was just a goof, which is why it has all the silly K-alliterations. These six young men were described as "college age" in 1865, which means they probably weren't even old enough to register to vote at all, as if that would have been a priority during and just after a civil war. The KKK was soon infiltrated and taken over by vigilantes who were
already active in the South, bent on continuing the War and engaged not in politics but in social structures. It was one of a dozen or more local and regional groups doing the same thing. It was wiped out by 1880, mostly by President Grant and federal pressures.
Then it was re-founded in 1915 by a Georgia salesman named William Simmons -- again no political affiliation and Simmons constantly insisted it was a "social club". Nevertheless it hired on some PR people and grew itself enormously, to the point where it had major impact; at one point it was estimated that one-third of the adult male population of Indiana was Klan.
And these references to Illinois are misdirected descriptions of Indiana. That's where D.C. Stephenson was from, the guy who engaged in a power struggle with Simmons to commandeer the Klan and take over. And yes Stephenson was a Republican, and I believe also a Democrat, whatever would suit his purpose at the time (like Donald Rump) but that isn't significant; it's just an avenue to power, which is all a political party is. Matter of fact at the time, Klan influence got a governor elected in Indiana and a governor and Senator elected in Colorado, as well as city offices in Anaheim and Portland Oregon, all of whom were Republicans, while also getting a Senator in Indiana and other officials in the South elected as Democrats. Whatever worked as an avenue to power. That's it.
Meanwhile amid all this popularity that drew membership in Indiana and Kansas City, the leading voice opposing the Klan was one Senator Oscar Underwood, a leading candidate for President in 1924, and a Democrat. The so-called "Klanbake" at the Democratic convention of that year was organized to keep Underwood from getting the nomination, and also to keep it from Al Smith of New York -- because Smith was a Catholic. A couple of years earlier the Klan had pushed successfully to impeach the governor of Oklahoma (Walton) after he tried to drive the Klan out of that state. Walton was also a Democrat. Four years later in 1928 the Klan again tried to keep Smith out of the nomination, but by then was waning in influence, largely due to Stephenson's rape-torture-murder scandal, and they failed.
So this specious latter-day revisionist association between the Klan and a political party can be shot full of holes with myriad examples, and has been.
As for LBJ and that fake quote about "having ni66gers voting Democrat for the next 200 years" reported by a grand total of one (1) book author, fun fact: the first President to prosecute the Klan since Grant was .... Lyndon Johnson.