Politicians don't like to reveal physical problems. In fact, they don't even like to wear overcoats, which might suggest that they get cold like us ordinary mortals. So, it's no wonder that British prime minister has made light of recent medical problems. In October, Mr. Blair was in the hospital suffering from an irregular heartbeat, and last week, he was back suffering from severe back pain. Keeping a stiff upper lip, the press office at 10 Downing Street insisted that Mr. Blair's back troubles have not caused him to miss a single engagement.

And yet. The strains of public office are showing on Mr. Blair, now in his third term. British voters returned the Labor Party to power on May 5 with a sharply reduced majority of 66 seats in the House of Commons, with both the Conservatives and the Liberal Democrats making significant electoral gains. Though a clear Labor victory, it was not exactly a triumphant endorsement of Mr. Blair's seven years in office.

As a consequence, both the ruling Labor Party and the opposition Conservatives are considering their options for when Mr. Blair steps down. The likely time frame is six months to three years down the road. Labor activists, who have fiercely opposed the war in Iraq, would like to see Mr. Blair gone sooner rather than later. Chances are that he will stay through a British referendum on the European Constitution in 2006. What the British succession will mean for the "special relationship" between the United States and Britain, this country's best ally in Europe will be of great importance.

The man waiting in the wings of the Labor Party is Chancellor of the Exchequer Gordon Brown. In American terms, Mr. Brown is treasury secretary, the second most powerful office in the British government. He has been Mr. Blair's junior partner in government since 1997.

Mr. Brown has run the British economy very capably, in large part inspired by the American, indeed conservative, economic model, based on deregulation and labor market flexibility. Mr. Brown's first move in office, for instance, was to make to make the British Central Bank independent of the government, like the Federal Reserve. During his tenure, Britain has achieved lower levels of unemployment and higher growth rates, over 3 percent last year, than most Continental European countries. This very unusual achievement for a Labor government has ensured Mr. Blair's reelection twice.

Mr. Brown hails from Scotland and would be a different kind of partner for President Bush. He is intense, brooding, and very sharp. Mr. Brown knows the United States and usually spends summer vacations on Martha's Vineyard - though reportedly often in the company of Democratic strategist Bob Shrum, who helped John Kerry lose the 2004 election. Mr. Brown is fiscally prudent, believes in welfare-to-work programs, but is also committed to a strong welfare system. With his own hands on the levers of power, he might well veer further left than Mr. Blair.

Mr. Brown is also one of the driving forces behind British government's commitment to doubling international foreign aid globally and he has helped make this goal the centerpiece of the G-8 summit in Scotland in early July. On the war in Iraq, Mr. Brown backed Mr. Blair policy of support for the United States, though he would probably not be as strong a partner in another war. All this adds up to a pretty mixed picture.

British Conservatives, meanwhile, are looking at Labor's weaker showing as a chance to return to government in the next general election - after what will have been a Tory decade in the wilderness. Following the May election, Tory leader Michael Howard declared he would step down, which from an American conservative perspective is probably good news, as he managed to alienate the Bush White House so profoundly with his attacks on Tony Blair that Mr. Howard was barred from the Republican convention last summer. Contenders for the Tory leadership include former minister for Europe David Davis and Shadow Foreign Minister Liam Fox, both of whom are well liked in Washington and would make good partners for a Republican administration.

Invariably, British prime ministers have found it in their interest to maximize the British-American "special relationship," no one more so than Tony Blair. It is in the interest of both sides of the Atlantic to keep this relationship strong and healthy, which one hopes his successor will realize as well.

Helle Dale is director of the Douglas and Sarah Allison Center for Foreign Policy Studies of the Heritage Foundation.