Book sales must be through the roof.
Michelle's book "Becoming" is a #1 NY Times Bestseller. She was advanced $60 million for her book and it is projected to be the best selling memoir in history. She has written others and Barrack has written a few himself. They have an estimated net worth of around $135 million. Certainly much wealthier than when they first entered the White House.
He also receives a 6 figure pension. The money that they receive from speaking engagements, book signings and appearances is staggering.