From Media Matters:
O'Reilly, Miller falsely suggested Obama supported Prop 8
Summary: Fox News' Bill O'Reilly and Dennis Miller falsely suggested President Obama supported California's Proposition 8. After Miller described a call to his radio show in which the caller suggested that "had [Obama] been a California resident," he "would have voted for Proposition 8," O'Reilly stated that the caller "probably listened to The Radio Factor and then called you because we had said that." In fact, Obama opposed Proposition 8.