Here's this, from Wikipedia:
On March 6, 1970, during preparations for the bombing of an officers' dance at the Fort Dix U.S. Army base and for Butler Library at Columbia University, there was an explosion in a Greenwich Village safe house when the nail bomb being constructed prematurely detonated for unknown reasons. WUO members Diana Oughton, Ted Gold, and Terry Robbins died in the explosion. Cathy Wilkerson and Kathy Boudin escaped unharmed ... The bomb preparations have been pointed out by critics of the claim that the Weatherman group did not try to take lives with its bombings. Harvey Klehr, the Andrew W. Mellon professor of politics and history at Emory University in Atlanta, said in 2003, "The only reason they were not guilty of mass murder is mere incompetence. I don't know what sort of defense that is."Barack Obama appeared with Ayers on a panel on juvenile justice organized by Michelle Obama on November 20, 1997.
Obama now claims Ayers has been rehabilitated and he denies writing book reviews favoring Ayers' theories of criminal justice.
If the Democratic nominee's relationship to Ayers - who wished he could have done more to destroy the U.S. - doesn't make your skin crawl, I doubt anything would.