President Bush's decision to commute Lewis "Scooter" Libby's jail sentence was that of a man who had nothing left to lose except his dwindling band of allies in the bunker of a besieged administration.

In the midst of the general condemnation of Mr Bush today were the defiant cheers from conservatives - among whom Libby's case had become a cause celebre. With scarcely 18 months left of his presidency remaining and his approval ratings at their lowest level ever, Mr Bush has retreated to this inner core of supporters.

The court decision earlier this week to turn down Libby's request to delay the start of his sentence, pending an appeal, may have forced the hand of Mr Bush who otherwise might have preferred to wait until after 2008 election. But equally important was last week's collapse on Capitol Hill of a bipartisan Bill to give illegal immigrants a path towards citizenship. Mr Bush's backing of that measure had badly strained relations with the conservative wing of the Republican party. By blocking the proposals, they effectively ended any lingering hopes the White House may have harboured of achieving a significant legislative legacy in his final years of office.

The president, however, still needs conservatives if he is to fend off renewed efforts by a Democratic-led Congress for an early withdrawal of troops from Iraq which would confirm that the war he embarked upon four years ago had ended in defeat. While the people criticising Mr Bush today are mostly those who bash him every day, he could not afford to lose his remaining loyalists, many of whom had been vociferous in calling for a full pardon of Libby. They had been watching carefully to see what Mr Bush would do in a case which echoed their own feelings of victimisation in the face of a vengeful liberal "establishment" over the Iraq war. The president's decision was regarded as a test of his courage, even faith. Although Libby was convicted of obstructing justice, rather than directly leaking CIA operative Valerie Plame's identity to the press, the issue behind the prosecution touched on the arguments that had been made for the invasion of Iraq. Ms Plame's husband, Joseph Wilson, had questioned the truth of claims that Saddam Hussein had weapons of mass destruction. Such disloyalty, loyalists reasoned, deserved a response in kind. The question remaining was whether Mr Bush would look after those, like Libby, who laid his own reputation on the line for the cause.

For all this, Mr Bush appears to have been mindful of his past condemnation of presidents using their power to keep people out of jail. Chief among these was Bill Clinton's hugely contentious pardon of Marc Rich on his last day in the White House - after the financier's wife had just donated to his presidential library. This probably explains why the President chose to commute Libby's jail sentence - leaving intact the conviction and fine - rather than give him a full pardon. (It did not stop, of course, Mr Clinton's wife, Hillary, from leading the cries of outrage yesterday.) Libby's 30-month sentence was by no measure extraordinary for the charge of obstructing justice but many legal experts believe his punishment was more severe than it would have been for others in the same circumstances.

Mr Bush's reasoning that Libby's sentence was "excessive" will puzzle those who remember his time as Texas governor. In those six years, 150 men and women were executed, a record for any governor in modern American history. In his book, A Charge to Keep, he described how he dealt with last ditch pleas for clemency. "I would ask: is there any doubt about this individual's guilt or innocence? And, have the courts had ample opportunity to review all the legal issues in this case?" Not much room for consideration of "excessive" punishments there. Indeed, one account tells how he mocked Karla Faye Tucker, a woman executed in Texas for a double murder despite becoming a born again Christian in prison. She had given a television interview asking for her life to be spared. Mr Bush parodied this in a whimpering voice. "Please," he said, pursing his lips in mock desperation, "don't kill me."

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