But that version of the story is too harsh. Mr. Bush is disagreeing with Mr. Blair not because he is a poor friend. He is disagreeing because he is a good one.

Consider the reasons for disagreement, which start with the familiar procedural problem. Yes, during war the US president is the commander-in-chief. But the three-branch system is still the law. Even if Mr. Bush wanted to go along on more extensive aid, Congress might not go along. The same holds true for regulatory concessions on global warming. The US Senate punished Bill Clinton, Mr. Bush's predecessor, for daring to consider the Kyoto treaty by voting overwhelmingly against the very concept of the treaty.

But there are deeper reasons Bush will not back Blair. The US, along with other countries, has signed a declaration to increase aid to 0.7 per cent of gross domestic product, something like $80bn in the American case. Other countries have criticised the Bush administration for not producing a plan to show how it will meet that goal. But the administration believes that democracy is the best form of aid in the long run, and that it is in Iraq and Afghanistan to bring about democracy. It believes these things so strongly that it is willing to send soldiers to corners of Iraq and Afghanistan from which even the most courageous aid groups have withdrawn. The Senate recently passed legislation for additional military spending. The amount of that spending was $80bn. In other words, Washington is doing its part.

The second reason for Mr. Bush's hesitation, at least when it comes to government-to-government aid, regards efficiency. Since September 11 a pious conviction has overcome the development world. The new belief is that because the stakes are now higher (al-Qaeda, tsunamis), five decades of experience regarding aid and development may now be ignored. In the case of Mr. Blair and Gordon Brown, his chancellor of the exchequer, the view seems to be that it is un-Christian -- ie, unforgivable -- not to spend more on aid. If George can be "Christian", and the new era is a Christian one, well then, Britons can be Christian too.

But here Mr. Bush, so disparaged for his emotional displays of faith, is acting as logically as the most analytic Brit. He is demonstrating awareness that September 11, for all its horrors, does not alter the essential flaw of state aid: that governments use it for purposes for which it is not intended. "When the World Bank thinks it is financing a power station, it is really financing a brothel," as Paul Rosenstein-Rodan, the great economic scholar, once put it. In his first term Mr. Bush therefore created the Millennium Challenge, according to which the US would give more only if there were concrete improvements in recipient countries. Now he is also more cautious about aid than some other national leaders.

An illuminating report published this past week by a network of international think-tanks -- including African ones -- provides support for Mr. Bush's position. Fredrik Erixon, its author, systematically reviews aid projects of the last half century and finds that heavy aid has correlated with slower growth in Africa.

In other words, everybody is being consistent. Mr. Bush is not going along with Mr. Blair in regard to aid because he does not agree with him. Mr. Blair went along with Mr. Bush in regard to Iraq because he did agree with him. The critics may have called Mr. Blair a lapdog. But his decision to back the US president came out of personal conviction that Saddam Hussein had to go.

In Britain, the general assessment is that this was unwise of Mr. Blair. And that he looked the fool because of later revelations about Iraq's nuclear capabilities. The conventional wisdom also holds that Mr. Blair must pay because the Iraq outcome hurt Labour in recent elections.

In American eyes, by contrast, Mr. Blair's willingness to defend unpopular positions means that he ranks even higher. Indeed, some Americans rate Mr. Blair above Mr. Bush. When the Pew Research Centre polled citizens in May, they found more Americans believed that Mr. Blair would "do the right thing" in confronting an international challenge than believed Mr. Bush would.

In short, the Blair-Bush alliance is not born out of mutual weakness but rather out of mutual strength. Mr. Bush and Mr. Blair are friends because they have something in common: they both believe in principle. Isn't that the strongest kind of friendship?

Amity Shlaes is a columnist with the Financial Times.