It should come as no surprise he hails from Mississippi (and was endorsed by Sarah Palin). From The New Republic:
Republicans and movement conservatives take great umbrage at any suggestion that the party’s electoral coalition includes a troublingly influential faction of resentful white reactionaries. They may often lie dormant, but McDaniel’s likely victory is their latest clinical presentation. And if McDaniel prevails in the runoff as expected, the Republican party will continue cry foul anytime a liberal makes this observation, while spending as much money as needed to get him elected.