When he was elected in 2000, Minnesota Democrat Mark Dayton seemed well prepared, having worked as an aide to Walter Mondale in the 1970s. But he has exhibited erratic behavior since then: ...In February Dayton, 59, made another notable blunder. The Mayo Clinic, which is in Rochester, Minn., was opposed to a South Dakota — based company's plan to expand its railroads into Rochester because it would mean dozens of trains passing by the clinic each day. Dayton told FORTUNE magazine the Mayo Clinic is "worth a hell of a lot more than the whole state of South Dakota." He...