- Obama's chance to save Europe comes at a London news conference with British Prime Minister David Cameron
- Anxiety about the possibility of a British exit from the E.U. is troubling the foreign policy establishment in Washington
(CNN)Franklin D. Roosevelt sent vast armies across the Atlantic. John F. Kennedy thumbed his nose at communism in Berlin. And Ronald Reagan chose the same iconic city to call on Mr. Gorbachev to "tear down this wall."