Colin Powell used to have a framed quotation from Thucydides in his office when he was chairman of the US joint chiefs of staff under the first President Bush: "Of all manifestations of power, restraint impresses men most".
Yesterday's announcement that Mr Powell is to resign as Secretary of State is not unexpected; but it does signify that President Bush was not minded to persuade him to remain. His departure removes the major voice of realist, moderate Republicanism from the administration. Politically and historically he will be judged by the extent to which he in fact managed to restrain the Bush administration's aggressive unilateralism over the last four years. All eyes will now be on whether his successor is chosen from a similar wing of the new administration or from the ranks of the hawks who despised and undermined him over the last four years.
Mr Powell has always valued loyalty as a political virtue and certainly extended it to Mr Bush by disguising his frustration over the direction of US defence and foreign policy - and perhaps by delaying his resignation until after the election. When appointed he was used as an example of the compassionate, centrist conservatism which would inform the Bush administration. It was a deceptive message. Even before the 9/11 attacks a whole series of international treaty obligations had been repudiated. After them US foreign policy was transformed.
Mr Powell helped create an international coalition to pursue those responsible in Afghanistan. Over the following year he went along with the hawkish surge to attack Iraq on a pre-emptive basis. Famously, he presented the US case that Saddam Hussein had weapons of mass destruction and was co-operating with those responsible for 9/11 to the United Nations Security Council on February 5th, 2003. It has since been shown conclusively that both of these cases for going to war were false, leaving Mr Powell's credibility in disarray. Nor was he able to win the argument within the administration for a much greater commitment to rebuilding Iraq after military victory.
These failures, and the associated falling away of US legitimacy and regard internationally make a convincing case that Mr Powell was not able to restrain the hawks. Alongside that record his early success in calming the US response to China's shooting down of a US spy plane, or his later holding of multilateral channels open from US friends and allies to a more and more unilateral administration are modest successes indeed.
President Bush has fateful decisions to make about the direction of his new administration and its leaders - and none more so than in the State Department and the Pentagon. Relations with Europe, the Middle East and Asia will depend in good part on who he appoints to these posts. It will be difficult to find someone of Colin Powell's stature, even if Mr Bush wants to see continuity to repair this political and diplomatic damage. The dove departs a hawkish administration.