President Obama has single-handedly kept thousands of American workers in their jobs by spawning dozens of best-selling books about how awful he is.  He can ignore almost all of them, and so can you, if your goal is to learn something new about the Obama presidency. But every once in a while, a book comes along that it would be foolish for Obama, or anyone else, to disregard. Vali Nasr's The Dispensable Nation: American Foreign Policy In Retreat, is the most trenchant criticism of the Obama administration I've yet read. ...