Trump's supporters have taken to pointing out that Trump disavowed David Duke and the KKK both before and after the Jake Tapper interview, as if that really addresses the issue. The problem is not that anyone really thinks that Donald Trump is a member in good standing of the KKK. The problem is that Trump is accused - with good and well founded reason - of playing wink and nod with white supremacists, and the fact that he refused to disavow the KKK in such a prominent spot adds more fuel to that fire.
The issue, put simply, is that it's a very simple question: do you disavow David Duke and the KKK? The answer is always "Yes," without waffling and qualifications. No matter how many times you get asked the question. There isn't a number of times you can say "yes" that even one "maybe not" answer becomes okay. If you're tired of being asked the question, then by all means say you're tired of being asked the question. Then say yes.
This is not hard, for anyone who isn't trying to intentionally court the white supremacist vote. The white supremacists know good and well that you have to disown them at some point. There's a reason they are anonymous, even on twitter - they disown themselves (even though Trump has allowed them all to come out and play tough guy). But they very well believe that what Trump did on Sunday was a sly wink that he's with them, much like the fact that he habitually "accidentally" retweets them on twitter.
That Donald Trump has in the past disavowed David Duke and the KKK does not mitigate failing to do so - even once - on national television. It's like those public service commercials about crystal meth - embracing the KKK: not even once.
Everyone else in America knows this, except for Donald Trump. And that's the problem.