First Lady Michelle Obama said her husband — a recent singing sensation — doesn’t hesitate to “show off his lungs” and sings to her all the time. President Obama proved his vocal ability when he sang a few lines of Al Green’s “Let’s Stay Together” at a campaign event earlier this month. ”That was completely spontaneous,” Mrs. Obama told Jay Leno in an interview on NBC’s “The Tonight Show” on Tuesday night. “I didn’t even hear about it until it got on YouTube, but he does have a beautiful voice, and he sings to me all the time.”