They do, but bringing them up makes us look like a bunch of racist a-holes. Better to oppose Obama on policy grounds so that we're not open to the accusation.
Only to the terminally PC, who think we're racist a-holes regardless of what we say. We're engaged in a global war with Islam ("radical Islam" is a redundancy... there is no moderate Islam). If there's verifiable evidence that Barack Hussein attended a wahhabi madrasa in Jakarta, and that evidence is boradcast far and wide, he's toast.
And if he's not on that basis, then we are.