Washington (CNN) — Former President George W. Bush and Michelle Obama are surprisingly close considering their political differences, and the 43rd president credits the former first lady's appreciation for his sense of humor as a key reason. The unlikely pair have often been photographed together during formal events. When Obama embraced Bush at the opening ceremony for the Smithsonian National Museum of African American History and Culture last September, the photo of their warm interaction went viral. "When I saw her, it was a genuine expression of affection," Bush told People magazine as he reflected on the moment. The interview...