Winning Britain’s elections was hard enough, now Prime Minister Tony Blair must sharpen his mind on Europe.Defeat in a planned 2006 referendum on the EU Constitution could bring his downfall, analysts say. Polls show most Britons oppose the Constitution. But France could take the heat off Blair if it rejects the treaty on May 29. If the French say ‘yes’ to the Constitution, Blair is said to be ready to appoint a UK referendum minister. The UK will hold the rotating EU presidency for the second half of this year. If the French say ‘no’, after his years of Britain-at-the-heart-of-Europe promises Blair will be EU crisis manager number one.