My favorite response: "You know this, how?"
At first I was irritated at the news for giving these types of folks so much of attention, as if their arguments had any merit. Then I realized what a boost they are for the democrats. The more they out themselves as ignorant, the less likely middle-of-the-road voters will be on their side come the next election.
So long as improvements are made with no major setbacks, his job is pretty much secure for the next term.