It's a dilemma. Originally, the decision was to cater a bit to racists and neo-Nazis, thinking they could be controlled and satisfied with a bone tossed to them every now and then.
But now the republicans can't win without them, and they know they have the party captive. If he does the right thing, Ryan will likely be replaced before too long with someone more acceptable to David Duke.
I don't know. I didn't think I was overestimating Republicans, but I was shocked how far they've been willing to let Trump go. I can only assume that they determined that they couldn't win without Trump, but this election should show them that they also can't win with him. Which makes me suspect that there's a lot more leaverage out there.