Mike Castle is a moderate Republican (I thought they'd all been purged from the GOP by now - you live and learn) from Delaware. Former Governor and current House Representative from Delaware.
He got booed in his own state for declaring that President Obama is a US Citizen. The Washington Independent has the story:
A little evidence that [the birther] conspiracy theory is showing up in uncomfortable situations for Republicans: Here’s Rep. Mike Castle (R-Del.), a moderate Republican who hasn’t announced whether he’s running for re-election or for the U.S. Senate next year, at a town hall meeting earlier this month.
A woman gets up, holding a baggie containing her birth certificate, and unleashes a rambling, minute-long tirade tirade about how the president is a “citizen of Kenya.