He voted for the Iraq war. Three years ago he won the Semper Fidelis award of the Marine Corps Foundation. He’s no leftie and no anti-war Bush-hater. Almost every week he visits wounded soldiers at military hospitals in Washington. But last Thursday he went ballistic.

Here’s what he said: “The war in Iraq is not going as advertised. It is a flawed policy wrapped in illusion. The American public is way ahead of us. The United States and coalition troops have done all they can in Iraq, but it is time for a change in direction.

“Our military is suffering. The future of our country is at risk. We cannot continue on the present course. It is evident that continued military action in Iraq is not in the best interest of the United States of America, the Iraqi people or the Gulf region.”

Murtha called for the immediate withdrawal of troops.

His stunning change of heart followed the passage of an amendment in the Senate last week that represented yet another sign that President George W Bush has essentially lost control of the capital: 79 senators supported the proposition that 2006 be designated “a period of significant transition to full sovereignty . . . thereby creating the conditions for the phased redeployment of United States forces from Iraq”.

It would be one thing if the vote was carried only by the anti-war Democrats, or the more cowardly anti-Bush and therefore anti-war Democrats. But it was also supported by many Republicans.

The Republican base is cracking over the war. It’s cracking simply because the president has so far been unable to persuade his own supporters that he is winning it. Fully two-thirds of Americans say the country is headed in the wrong direction. But the real news is that, in one poll last week, 41% of Republicans agreed with that proposition, a 12-point jump from the month before.

The anxiety on his own side, allied to the hostility of the opposition, means the results are not pretty. Bush’s approval ratings are now in the mid to upper thirties. The Wall Street Journal’s poll last week put him at 34% approval. At the same time in his second term, Richard Nixon had 37%.

Worse, Bush’s disapproval ratings are high and have lasted longer than any recent two-term president. As the blogger Chris Bowers notes, no other two-term president with Bush’s persistent disapproval rating has recovered.

The silver lining is that the public doesn’t like the Democrats in Congress either. They have a 25% approval rating. This truly is a winter of American discontent.

The depth of Bush’s vulnerability was manifested last week by the counterattack by the president and vice-president. Instead of laying out a concrete strategy for winning the war — plans to improve and accelerate the training of the Iraq army, to rid the military of detainee abuse, to control Iraq’s borders more effectively — Bush and Dick Cheney decided they had to defend themselves against the charge of pre-war deception.

I agree with them that the evidence does not support the idea that they deliberately misled anyone. But the fact that they are still trying to persuade the public three years later and at a critical moment in the Iraq campaign is a sign of desperation, not strength.

There will be many who will take satisfaction in some of this. But the stakes are surely too high for schadenfreude. The war in Iraq is not like Vietnam in one critical respect. Abandonment of the Vietnam war did not tip the balance towards the Soviet Union in the cold war. Abandonment of the Iraq war would indeed mean a massive victory for the forces of terror and jihadism across the globe, threatening every Arab regime and every free western citizen.

What the Senate did last week was signal to Abu Musab al-Zarqawi that he only has to wait the US out. It’s one thing to hope that we will be able to withdraw troops next year. It’s quite another to announce that we will. Nothing could be more harmful for the possibility of success in Iraq. And failure is not an option.

It may be, of course, that this lever paradoxically works in America’s favour. Hey, I’m trying to be positive here. The threat of American abandonment might concentrate the minds of Iraqi politicians and help them bury sectarian division in the face of a more terrifying alternative: jihadist tyranny.

The parliamentary elections in Iraq next month could prove a turning point. The training of the Iraqi army seems to be progressing slowly. If the Democrats win big in next year’s congressional elections they might be forced to shake off their flirtation with left-wing foreign policy and anti-Bush opportunism and try to develop a sound strategy for winning the war. (And, yes, despite their low approval numbers, they could still win. Those numbers reflect in part disillusion among their own base — who will vote Democrat anyway. And polling data on congressional voting currently give the Democrats a double-digit lead. Even gerrymandering might not be able to resist that tide.)

For the moment, however, we have a war we cannot afford to lose being run by a president who has essentially lost the confidence of his own people. Bush must do something to regain it. But in the last year he has provided scant evidence that he can; and history suggests he won’t.

Resilience in the war will therefore depend on Republican senators like John McCain and Lindsey Graham and Democratic senators like Joe Lieberman and even John Kerry, who distanced himself firmly from Murtha last week. They are the effective leaders of the war on terror now. We can only hope they will prove more successful than the man nominally elected to prosecute it.

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