That sharp tongue would’ve come in handy. But the day after being applauded for a fine debate performance, the GOP front-runner let a supporter’s comment — calling President Obama a Muslim who’s “not even an American” — slide at a New Hampshire rally. The man declared, “We have a problem in this country. It’s called Muslims,” to which Trump said … almost nothing. He simply responded vaguely to a question the man posed about militant training camps, which is bound to draw fire, not least from the left.