One of Barack Obama’s finest moments in the long campaign of 2008 was when he mocked Hillary Clinton and John McCain’s call for a “gas tax holiday” to curb rising petrol prices. “It’s a stunt,” Mr Obama said before the primaries in North Carolina and Indiana, where Mrs Clinton was making her final stand. “It’s what Washington does.”

Four years later, America faces the prospect of another summer of rising prices and an election that could hinge on how far they go. The world oil price has risen by almost 30 per cent since October. A further jump of 20 per cent would take it above $150 a barrel, which would endanger America’s recovery. In the past few days US pump prices have been inching towards $4 a gallon – a traditional panic threshold for consumers and therefore also politicians.

How big a menace does this pose to the president’s re-election prospects? And what, if anything, can he do about it? The threat to Mr Obama is political and economic. On the politics, voters have recently started to complain. Last week, two-thirds of those polled told CBS that their finances had been hit by recent price increases, of which almost 40 per cent reported their hardship was “serious”. More ominously for Mr Obama, a large majority said the president has the power to do “something significant” about it – in Mr Obama’s dreams, one imagines.