As his heart failed a couple of summers after leaving office, former Vice President Dick Cheney slipped into a coma and, by his later account, spent weeks dreaming that he was in a countryside villa north of Rome, padding down a stone path every morning to pick up a newspaper or coffee.

Yet Mr. Cheney was never one to slip into quiet retirement in Italy or, for that matter, at his Wyoming ranch. Two years after a heart transplant reinvigorated him physically, he seems reinvigorated politically, too, as he takes on President Obama, Hillary Rodham Clinton, Bill Clinton, radical Islam, Senator Rand Paul, his own party — and history.

Frustrated by what he considers the president’s weakness as extremist groups seize wide portions of Iraq, Mr. Cheney, 73, has blitzed the airwaves in recent weeks and formed a new organization to promote American national security in a perilous time. He has drawn nothing but scorn from Democrats and even some Republicans who view his remonstrations as the height of hubris from someone they blame for many of the country’s difficulties. To them, he is a punch line.

But Mr. Cheney’s ability to command attention speaks to his distinctive place in the public arena. He is blunt, he is unapologetic and he is seemingly immune to the barbs aimed his way. He remains driven by the attacks of Sept. 11, 2001, and determined to guard the nation against the dangers he sees. If the rest of the world has moved on, he has not. “I’m not running for anything,” he told Charlie Rose in one of his multiple interviews of late. “I get to say exactly what I think.”