By accident of its birth -- a collection of separate colonies that slowly came together to form an independent union and revolted against the remote power of the British government -- the United States has an enduring bias toward localism, an aversion to centralized government that is part of its DNA. For some on the left, this has been seen as a positive. "It is one of the happy incidents of the federal system that a single courageous state may, if its citizens choose, serve as a laboratory; and try novel social and economic experiments without risk to the rest of the country," Justice Louis Brandeis once wrote.