Flip through any list of Republicans running for president or probably running or maybe thinking of running, and you'll find at least a couple dozen names. From Mitt Romney and Tim Pawlenty to Michele Bachmann, Rudy Giuliani, and Donald Trump, it's a potentially vast field peppered with outsize personalities and also folks who make you say, "who?" Why so many? "Because people perceive vulnerability in President Obama," says Darrell West, a political analyst at the Brookings Institution. "We have high unemployment, we have 2-1/2 wars, and there's a lot of contentiousness surrounding health care. So nobody's afraid to take on...