In the three months since leaving office, Mr. Cheney has upended the old Washington script for former presidents and vice presidents, using a series of interviews — the first just two weeks after leaving office — to kick off one last campaign, not for elective office, but on behalf of his own legacy. In the process, he has become a vocal leader of the opposition to President Obama, rallying conservatives as they search for leadership and heartening Democrats who see him as the ideal political foil....

Other former vice presidents have kept a much lower profile, at least this early after leaving office. Al Gore was supportive of Mr. Bush after the Sept. 11, 2001, attacks, but in September 2002 delivered a speech critical of Mr. Bush’s plans for the Iraq war. After John F. Kennedy bungled the Bay of Pigs invasion in April 1961, Richard M. Nixon, the former vice president who lost to Mr. Kennedy, visited the new president at the White House and said the nation should support him.

But some conservatives, feeling beleaguered these days, are grateful that Mr. Cheney is speaking out. John R. Bolton, a former ambassador to the United Nations and a close ally of his, said that after having to hew publicly to Mr. Bush’s views, Mr. Cheney might be feeling liberated. “It’s about time he had a chance to get his voice back,” Mr. Bolton said. “There’s no cone of silence now.”