Why did the republicans laugh when asked 'Who's Gonna Shoot Obama?'?

Ok, this is, admittedly, a highly inflammatory kind of question, but I am interested in the psychology of the situation. A report at TPM said that even the Congressman laughed when this question was asked. Was this nervous laughter? He responded, “I know there’s frustration with the President…”

What’s going on here? Is there some underlying animosity with the President that makes some conservatives assume he’ll be killed? Why would they be like that? Can you explain what they could have been thinking? Is this proper behavior for true patriots? I.e., the President is so bad, he should be killed? Is it for real, or is it, as the Congressman responded, just the rhetoric of frustration?

For extra points, if you were the Congressman, how would you have responded?