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Click image to see more photos. (Jacquelyn Martin/AP) WASHINGTON—It's not every day that Washingtonians have to fight for an open chair at the Brookings Institution for a Wednesday-afternoon foreign policy event. But since it was Florida Sen. Marco Rubio doing the talking, two days after a campaign trail appearance with Mitt Romney, the think tank had a barnstormer on its hands. Rubio, a young, charismatic Republican at the center of speculations over Romney's running mate, arrived onstage with Connecticut Sen. Joseph Lieberman, a former Democratic vice presidential candidate, to show off his foreign policy chops. Because of this guessing game, almost every word Rubio utters in public from now until the moment Romney makes his choice will be dissected, prodded and scrutinized. Whether he likes it or not, events like these are the start of a long spring training. Every seat was filled, with reporters and onlookers lining the walls. An overflow space with the speech...