During an occasionally hard-hitting speech at today's National Prayer Breakfast in Washington D.C., President Barack Obama drew laughter and applause from the bipartisan crowd when he cracked a "Birther" joke, the first time he's acknowledged persistent rumors and lawsuits asserting that he's a Muslim born in Kenya (watch clip below). Some on the right have criticized the president for the joke, saying questions about his citizenship "go to the core of the American republic," while liberals are urging Obama to ignore such "nonsense."