At General Motors, they used to call their surging competitor "Mr. T," as if intimidated by a muscular rival who seemed able to seize market share at will. But Toyota suddenly looks pretty meek, thanks to a mystifying safety problem that has led to a huge recall, an unprecedented production shutdown, and an ugly dent in a once sterling reputation. This corporate nightmare has mushroomed since last fall, when Toyota recalled about 4 million vehicles because of floor mats with a propensity to slip down into the driver's side foot well, potentially interfering with the pedals and causing sudden acceleration....