The action against Osama bin Laden, the Taliban regime and global terror has begun. And in the hazardous days ahead President Bush will have no stronger ally that Mr Blair.
The British Prime Minister returned from his latest 5,000 mile diplomatic odyssey - this time Russia, Pakistan and India - his sinews stiffened anew. Those travelling with Mr Blair had felt the increased sense of urgency, the imminence of military engagement.
As it got under way last night, Mr Bush confirmed that British servicemen were there at the beginning. He had already vowed to stand "shoulder to shoulder" with the American people to the last.
Those Britons watching the burning of Mr Blair's effigy in Peshawar may have felt a shiver of apprehension. They understand only too well the Metropolitan Police Commissioner's conclusion that Britain, as America's biggest ally, can expect to be next in line for attack.
Which of course is Mr Blair's first line-of-defence for his commitment to this "war" unlike any Britain has ever known. Again last night in Downing Street Mr Blair defined the British interest in terms of the damage and uncertainty inflicted on the global economy by the September 11th attacks. He cited the fact that 90 per cent of all the heroin on Britain's streets is believed to come from the poppy fields of Afghanistan.
Over and above all this, however, the Prime Minister's belief that his country's vital interests are at stake is rooted in his conviction - strengthened if anything by his talks with Gen Musharraf - that Bin Laden and his terrorist network are prepared to attack anywhere, at any time, and that "they know no limits". "It's not just us against Bin Laden," stressed a British official last night: "It's us against the terror network."
But it's also about maintaining the political, diplomatic and humanitarian coalition, it's about re-invigorating the Middle East peace process."
That has been a striking and consistent line from Downing Street from the outset. And while Mr Blair's aides reject any suggestion that his instant declaration of support was an attempt to rein-in American hawks at a stage when the US might have been tempted to "lash-out", there is little doubt here that the British Prime Minister has played a vital role in building the extraordinary coalition. For all its inherent tensions and potential contradictions the coalition meant that Mr Bush was able to call in Mr Blair's aid when he addressed the American people last night.
Even before last Tuesday's Labour Party conference speech, when Mr Blair outlined his global ambitions and his belief that good should come from the evil of the atrocity in America, there was mockery of Mr Blair's increasingly "presidential" demeanour. It was a mockery fuelled in some cases by an instinctive anti-Americanism on the British left which Mr Blair said shamed those who felt it. There is unease at the embrace of President Putin and enforced memory lapse over Chechnya, as of Gen Musharraf's nuclear-tipped regime in Pakistan.
And there is, not least in the Labour Party, a suspicion that this Prime Minister prefers the role of world leader in a time of international crisis to the detail of domestic policy on which elections invariably turn.
With British troops now engaged, those dissenting voices will fall silent - at least for now. The left may shudder at the Wall Street Journal's depiction of Mr Blair as "America's chief foreign ambassador to members of the emerging coalition".
Many more in Britain instinctively recoil from Mr Blair's missionary fervour when he talks of Jews, Muslims and Christians - "all children of Abraham" - as he defines his moral purpose. However that will hardly diminish their shared sense of ownership of it, or their determination that it should prevail.