What if a president gave an applause line and no one applauded?

I happened last night at the beginning of the presidential debate. President Obama probably didn't hear Jim Lehrer's admonition to the audience to keep quiet after the introductions and hold their noise until the end. To the audience's credit, they did, at least in the parts I saw.

So both Romney and Obama got introduced and both got their applause. Then the debate began with Obama getting the first question. He began his response with a heart warming shout out to his wife about their anniversary -- an applause line if there ever was one. The audience sat in silence. Obama's grin faded into a stunned look. That night was probably the first time in a long time, if ever, where he provided a crafted applause line and got back nothing.

It threw the cool one off balance, and he didn't recover.