A new book, Renegade, about Mr Obama's unlikely run for the presidency, recounts a tense period in 2000 when the Obamas' marriage was on the brink of collapse because of his restless political hunger and the family's shattered finances.
Charla says: "WHEN I offered my husband sex every day for a year to celebrate his 40th birthday he literally fell over. As I had spent so long thinking about an exciting present that I thought he would love, I was confident he would say yes..."