Five years ago, when John G. Roberts Jr. became the Supreme Court's chief justice, he described the job as though he would be a minor functionary, more like an umpire behind the plate than the star of the game. He also said he favored minimal and narrow decisions, rather than broad but divisive rulings that would abruptly change the law. But in recent weeks, Roberts has shown that when he has the support of moderate Justice Anthony M. Kennedy, he is willing to move boldly on behalf of conservative causes. Long-standing laws and precedents need not stand in the way.