Between his trip to Europe last week and his travels to Africa next week, President Obama is doing a lot of gift exchanges with foreign leaders. In the past, he has gotten mixed reviews. Four years ago, for giving the queen of England an iPod. Other presents have gone over better. But the president does not personally select these gifts — a staffer does. And there's a well-kept secret at the White House: When Obama wants to choose a gift himself for someone in his inner circle, he sets a very high bar. Last November, Valerie Jarrett, one of the...