WILMINGTON, Del. — On the eve of the primary that would end his electoral career, Rep. Mike Castle was in a reflective mood. He seemed calm and confident, yet almost everything he said sounded valedictory as he offered a prescient analysis that explained in advance a defeat that echoes through the nation. A genial and courtly man in the manner of the elder President Bush (who held a fundraiser for him in Kennebunkport), the nine-term congressman was mourning the decline of both the conciliatory style of politics that animated his career and the moderate Republican disposition that the Tea Party...