Blair's approval rating has slumped since committing British troops to the U.S.-led war. Some of his own lawmakers accuse him of being Bush's "poodle," and recent polls suggest a majority of Britons don't approve of their "special relationship" with the United States.
Opponents of the war hope to bring out tens of thousands of demonstrators to march against Bush's visit, which begins Tuesday night.
"It is a disgrace that Tony Blair is once again ignoring public opinion to entertain his friend at our expense," reads a campaign leaflet printed by the Stop the War Coalition, which has organized next Thursday's march through central London.
The timing of Bush's visit, planned 17 months ago, is difficult for Blair.
After a year dominated by international affairs and with national elections as little as 18 months away, the prime minister wants to concentrate on his domestic agenda and calm unrest in his governing Labor Party caused by the war.
His recent public appearances have been dominated by visits to schools, hospitals and down-at-the-heel public housing.
In this context, Bush's "arrival is about as appropriate as the appearance of a stripper at a wedding," The Guardian newspaper said in an editorial on Saturday.
Bush is clearly aware of Blair's predicament and heaped praise on him in a round of interviews this week. He also seemed to counter criticism that Blair simply took orders from Washington.
"He's plenty independent," said Bush. "If he thought the policy that we have both worked on was wrong, he'd tell me. He tells you what he thinks and he does what he says he's going to do. And that's about as high a compliment as I can pay a fellow leader."
Protesting his independence, Blair wrote in a Sunday newspaper that he had had differences with Bush.
"Where Britain's national interests are best served by airing them publicly — as for instance over our different positions on global warming or steel tariffs — I don't hesitate to do it," Blair wrote in the News of the World.
"And where behind-the-scenes diplomacy works best, I talk frankly in private to President Bush as I do to other leaders. But I welcome this visit because it's more important than ever to underline that our two countries share the same values, the same love of freedom and determination to build a safer world."
Britain has been Washington's most solid ally in the war against terrorism.
But the prime minister's decision to back the Iraq war, despite widespread opposition among the public and in the Labor Party, has cost him dearly. For the first time in his six years in office, he appears vulnerable.
Last month, a third of those questioned in an ICM survey were satisfied with the job he is doing as prime minister, while 61 percent were unsatisfied — his lowest approval rating since he swept to power in 1997.
Blair persuaded Parliament to back the war because of the threat of Iraqi weapons of mass destruction — and has been on the defensive for months because of the coalition's failure to find evidence of any.
The prime minister had "destroyed a large part of his international and domestic credibility by promoting a bogus claim that Saddam's weapons of mass destruction were a clear and present danger," former Foreign Secretary Robin Cook wrote in The Independent newspaper Friday.
"After all that, was it really necessary to throw in a white tie and tails dinner to convince George Bush that he is his friend?" asked Cook, who resigned from a different Cabinet post in protest at the war.
Jonathan Stevenson of the International Institute of Strategic Studies said there was no doubt the Iraq war had been deeply damaging to Blair are home. But with France and Germany vehemently opposing the war, the invasion also damaged his image as a "truly European prime minister," Stevenson added.
Blair says the European Union and Britain' strong ties with the United States are the twin pillars of his foreign policy.
However, in backing Bush over French President Jacques Chirac and German Chancellor Gerhard Schroeder, Blair had shown that "when push comes to shove the special relationship is more important than Britain's European identity" and he must now work hard to "restore his European credentials," Stevenson said.