The war in Iraq - never mind the troubled aftermath for the moment - was a victory for him. The British economy has weathered the long global economic slump better than that of any major European country. With less than two years to go before the next mandatory national election, only one-third of Britain's voters can identify Blair's conservative opponent.
But Blair's approval ratings are among the worst since he took office in 1997. That is in no small part because of the failure of coalition troops to find weapons of mass destruction in Iraq, and the subsequent erosion of his credibility.
The missing weapons are a much more prominent issue in Britain than in the United States. Blair's primary argument for leading his country into the war when sentiment was solidly against it was based on his insistence that Iraqi leader Saddam Hussein possessed the weapons and that they could get into terrorists' hands.
As recently as March 18, two days before the start of the war, Blair told Parliament: "We are asked now seriously to accept that in the last few years - contrary to all history, contrary to all intelligence - Saddam decided unilaterally to destroy those weapons. I say that such a claim is palpably absurd."
With no weapons found, Blair has been disarmed of his most potent political weapon: his ability to persuade people to trust him. He is under attack not only from opposition conservatives but also from members of his own Labor Party, including two of his former Cabinet ministers; and not only in reliably opposition conservative newspapers but also in the left-leaning press.
"At the root of the trouble he's having with all kinds of issues is Iraq and this loss of trust, which has always been his secret weapon," said David Baker, a professor of politics at Warwick University in London. "He has always been given the benefit of the doubt because of his ability to face the electorate and say, 'Look, I know what I'm doing on this issue, it's the right thing,' and people would trust him. There's no question that ability is not what it once was."
Blair's weakness was underscored yesterday when Iain Duncan Smith, leader of the Conservative Party and, at this point, Blair's likely opponent in the next election, took to the floor of Parliament during the weekly event known as "Prime Minister's Questions."
The question period is a political show, unlike anything in the United States, the equivalent of President Bush standing before Congress and being heckled and questioned by his opponents, and then having to provide answers to questions on everything from defense policy to transportation funding. The questions are a raucous time in Parliament, with hooting and hollering, even some hissing.
Yesterday, at three different points, Duncan Smith glared at the prime minister and then practically yelled: "Nobody can believe a single word he says anymore!"
The remarks were a direct attack on Blair's credibility and the trust-me persona he had used to great effectiveness - and they had nothing to do with the war in Iraq.
Instead, the remarks came over education funding, during a question about train service and during a proposal by Blair to do away with the position of Lord Chancellor.
"What you're seeing is the prime minister's opponents trying to widen what they perceive to be a crack in his veneer, if you will," said Nick Gilby, a political research analyst for MORI, Britain's largest independent polling firm. "They sense they have him on the run, and they will try to use what now appears to be misinformation about Iraq to argue every conceivable issue. Their message is, 'If he'll lie to lead the country into war about Iraq, what won't he lie about?'"
There are two investigations into how Blair's government used intelligence information in lobbying both Parliament and the public to support the war in Iraq. Tuesday, two former ministers, who resigned over the war, accused the government of distorting the intelligence information to manipulate public opinion.
Robin Cook, a former defense secretary who quit as House of Commons leader in March, said he had not believed that Hussein posed an immediate threat and that intelligence information backed this up. The lack of discovered weapons vindicates his belief, he said.
"Such weapons require a substantial industrial plant and a large work force," Cook told the Commons' Foreign Affairs Committee. "It is inconceivable that both could have been kept concealed for the two months we have been in occupation of Iraq."
Clare Short, who had threatened to resign her Cabinet post before the war but waited until the fighting ended, was more pointed, claiming Blair had purposely misled the country in what he saw as an "honorable deception."
Blair maintains that his decisions were based on information from the British intelligence service. He has called for patience, asserting that he is confident that weapons will eventually be found.
In the meantime, his proposals on issues that have nothing to do with the war are taking a beating. In his Cabinet reshuffle, an annual event in British politics, he proposed a U.S.-style Supreme Court, effectively ending the position of Lord Chancellor, which had been held by such historical figures as Sir Thomas More.
Duncan Smith likened the move to that of a "dictator," and in an unusual action, the speaker of the House of Commons called on Blair to issue a statement explaining why he was proposing the change. Almost without exception, newspapers have jumped on him for not consulting the queen or the opposition party. Blair has spent much of the past week trying to undo the perception that he botched the reshuffle.
"Before Iraq, there would not have been this kind of intense furor," said Warwick University's Baker. "He would have again said, 'Trust me,' and people would have. I think the reaction is very telling."
Few are suggesting that Blair's job is in danger. Elections are as much as two years off, and while Blair's approval ratings dropped nine points, to 38 percent, from April to May, the conservatives gained no support. In fact, only 34 percent of voters could identify Duncan Smith as leader of the Conservative Party, according to the most recent MORI poll.
"If the erosion in support were to continue, there might be cause for some alarm," said Gilby, the MORI researcher. "What the prime minister has going for him most right now is that the Conservative Party has nothing going for it."