Graham, McCain erupted into a violent fit. "He jumped up and down, screaming obscenities at us for at least 10 minutes," Silver said. "He shook his fists as if he was going to slug us." Witzeman left the meeting stunned. "To my mind," he said, "McCain's the most likely senator to start a nuclear war."

The last time anyone made that sort of charge against a senator from Arizona, it was about Barry Goldwater, who ran against Lyndon Johnson in 1964. A famously effective campaign ad showed a little girl picking a daisy, which then mutated into a mushroom cloud. Painted as a potential nuker of the planet, Goldwater lost in a landslide.

The US press has fawned over McCain the 'maverick' for years, but his colleagues in the Senate have long regarded him as a mere grandstander, posturing for C-SPAN's camera about wasteful spending, then meekly voting for the pork-barrel items he's just denounced.

They snicker at his affectations of moral purity, noting such seamy episodes as McCain's imprudent association with Charles Keating, an Arizona bank swindler, ultimately

convicted and sent to prison. They point to the torrents of money pouring into McCain's campaign treasury from the corporations that crave his indulgence as chairman of the Senate Commerce Committee.

In a damaging story suggesting ethical double-standards, the New York Times this week cited McCain aides as decrying their boss's unwise association - one they construed as possibly romantic - during his 2000 presidential bid with an attractive lobbyist, Vicki Iseman, then 32. The aides confronted Iseman (left), telling her to stay away. McCain denies any romantic involvement.

For such reasons it is foolish to think McCain will find it easy to put a shrewd debater like Obama on the defensive. And beyond such biographical impedimenta, the 71-year-old senator totters towards the autumn campaign under one huge burden which is not his fault. This week George Bush's approval rating sank to the lowest in the history of such polls, 19 per cent. A very large number of Americans have simply had it with a Republican in the Oval Office.