How did it happen? Why did David Cameron apparently rip up his own policy of positive engagement with Europe, as well as 40 years of British foreign policy?
"Parliament," one British official whispered to me in Brussels. In other words, Cameron was not prepared to stand up to Conservative Eurosceptics and force through the Commons a treaty to help save the euro - if necessary, with the votes of Labour and Liberal Democrat MPs. True, it would have been messy. There would have been ministerial resignations as well as a huge backbench revolt.
But Cameron accepted that saving the euro was in Britain's national interest. When it came to the crunch, it seems he put his party's interests first.
I have been watching British prime ministers at international summits since 1987. I saw Margaret Thatcher wield her handbag and John Major and Tony Blair veto the appointment of federalists as president of the European Commission.
Cameron went much further. He has broken Thatcher's law: always keep a seat at the table. She knew that was in the national interest.