Evidence of Trump dementia:
Trump in 2000 when he decided not to run as the Reform Party's candidate for President:
"The Reform Party now includes a Klansman, Mr. Duke, a neo-Nazi, Mr. Buchanan, and a communist, Ms. Fulani.."
http://partners.nytimes.com/library/politics/camp/021400wh-ref-trump.html
Trump in November 2015 when asked if he wanted David Duke's endorsement:
"I don’t need his endorsement; I certainly wouldn’t want his endorsement"
http://www.politico.com/story/2015/08/donald-trump-doesnt-want-david-duke-endorsement-121784
On Friday when told that David Duke endorsed him:
"David Duke endorsed me? OK, alright. I disavow, OK?"
http://thehill.com/blogs/blog-briefing-room/news/270931-trump-brushes-off-david-duke-support
Trump today:
"Just so you understand, I don't know anything about David Duke, OK?"
http://www.cnn.com/2016/02/28/politics/donald-trump-white-supremacists/
So, after knowing about David Duke since 2000 and reinforcing that he knew him as recently as Friday, Trump has forgotten all about him. Poor man will soon be unable to remember his own name at this rate.