The next election
Mr Obama could plausibly argue that a renewed crisis with its roots in Europe is hardly his fault. But such an argument would make him sound like he was weak, or searching for excuses. His Republican opponent could simply pose the old question – are you better off now, then you were four years ago? – and hoover up the votes of the majority of Americans who would reply, emphatically, No.
This raises two points that should be of interest and concern both to David Cameron and Ed Miliband. Cameron should bear in mind that, whatever advantage is bestowed on the Tories by Miliband's desperately weak leadership ratings, ultimately elections are more of a referendum on the incumbent than a choice between the contenders. Labour's weakness is a bonus for the Tories, but it isn't a clincher.
Miliband also has occasion to rue Cameron's luck. Obama won office just as the financial crisis crested - and will be standing for re-election while the aftermath still rumbles on. In the UK, the recession played itself out (in its first iteration at any rate) before the election, meaning that the hits to prosperity and income were largely suffered under the Labour Government. The Coalition, on the other hand, has presided over an uncertain recovery, rather than a full blown recession and can hope, by 2015, to be in full recovery. The question 'are you better off than in 2010' should be a much easier one for the electorate to answer positively in 2015 than 'are you better off than in 2008' will be in 2010.