The timing of the Istanbul bombs could not have been more telling.
Blair and Bush stand together
They came at the height of US President George W Bush's state visit. He and Prime Minister Tony Blair were about to give a joint press conference in the very seat of the UK Government.
London was already in a state of tension. Protesters were gathering, evidence of the divisive nature of their policies.
There was a mismatch between the pomp of the visit and the passion it had aroused.
Suddenly, the ground seemed to rumble under their feet.
For two men who have said they will make the world safe from terrorism, here was a reminder that the reach of al-Qaeda and its allies is still long.
They were clearly shocked but both resolutely declared that they would not be put in awe of such attacks.
Instead, there was Churchillian talk, especially from Mr Blair.
This was no surprise. It has for long been clear that Mr Bush has not dragged Mr Blair along with him. Tony Blair has been more than a willing partner.
One recalls, and the former US Secretary of State Madeleine Albright's memoirs have recently confirmed, that Tony Blair wanted to send ground troops into Kosovo in 1999. Bill Clinton did not.
Two quotations from him after the Istanbul attacks sum up his reaction:
"Once again, we must affirm that in the face
of this terrorism there must be no holding back, no
compromise, no hesitation in confronting this menace, in
attacking it wherever and whenever we can and in defeating
"Our response is not to flinch or give way or concede one
inch. We stand absolutely firm until this job
Mr Bush is more used to such attacks. He experienced 9/11.
Britain in front line
But now the British prime minister was confronted with the reality that Britain, too, is in the front line.
The attacks on British targets promised months ago by Osama Bin Laden had taken place. There might be more.
And they might come in Britain itself.
So what is to be done about it?
For a start, the US and UK have to put Iraq back together again.
That was a major point made by both men at the press conference. How to do it was a major point, too, in their talks.
"Our mission in Iraq is noble and it is necessary, and no act of thugs or killers will change our resolve or alter their fate. We will finish the job we have begun," said Mr Bush.
"It should not lessen... our commitment to Iraq. On the contrary it shows how important it is to
carry on until terrorism is defeated there as well," said Mr Blair.
The concept is that if Iraq can emerge from the current crisis with stability and a democratic government, it will remove one source of anti-Western hostility.
But of course, there are other sources.
That is why George Bush spoke so much in his speech in London on Wednesday about spreading "democracy" in what he has taken to calling the "Greater Middle East," which presumably means anywhere from Morocco to Yemen.
In the short term, there will have to be tighter security at British diplomatic buildings just as there have been at American.
Britain getting drawn in
The fact that Scotland Yard has sent a team to Turkey shows how Britain is being drawn into examining the local conditions from which so many of these attacks spring. The FBI has been doing the same for years.
A better understanding of how and why these attacks take place is needed.
In Turkey, for example, the suicide bombers who attacked two synagogues on 15 November were cousins from the town of Bingol in the south east where Islamic fundamentalism is strong.
One of them is said by Turkish reports to have been in Afghanistan and Iran some time ago.
These links indicate how al-Qaeda seems to combine both local and international factors.
Such links will have to be broken up but they are many.
The rest of the agenda
The Istanbul bombs completely overshadowed the rest of the Bush-Blair agenda.
No decisions were made on two of Mr Blair's concerns - the British detainees at Guantanamo Bay and the US steel tariffs.
On the first, talks are to continue over the two options - giving them military trials, to which Britain has objected, or sending them back to Britain.
Probably no decision will be taken until the US Supreme Court looks at the issue over the next few months. Mr Bush did hint that British objections would be taken seriously.
As for steel, the president simply promised a "timely decision".
He is now considering a report from the US Government agency the International Trade Commission on how the tariffs have affected not just steel-making but steel-using industries.
The tariffs are due to run until the end of March 2005. But having imposed them, it will be hard for Bush to lift them.