What is an example sentence in waif?
The waif looked at him with large eyes.
The waif was undernourished.
The waif was one of many homeless children.
Models are still expected to be thin, but in the 1990s the "heroin chic" look was all the rage, and you couldn't get a modeling job unless you were an 80-pound waif. He can weave the most insubstantial waif of truth into a veritable tapestry of propaganda. The stray kitten I adopted soon grew from a 1-pound waif to an 11-pound lapcat.
If you mean, who is his wife, then the answer is Michelle Obama. If the question is really asking about a "waif" of President Obama, since waif is often used to mean: "a person, especially a child, who has no home or friends", then the answer would have to be that he does not have one to our knowledge.