This week, most Americans will for the first time tune in seriously to Mitt Romney’s presidential campaign at his convention in Tampa. Most conservatives will probably like what they see – a pro-family, strong defence and small-government ticket that offers a clear alternative to a second Barack Obama term. Most liberals, however, will probably recoil from the Republican party’s demonisation of a president who took office in exceptionally tough circumstances. Weather permitting, the theatre should be compelling.

More important than the spectacle itself is whether Mr Romney and Paul Ryan can persuade voters they have a credible plan to revive the US economy. Executive competence is the core theme of Mr Romney’s biography. Taking the tough economic decisions is the hallmark of the Romney-Ryan campaign. On the evidence so far, the ticket deserves one and a half cheers. They are right to say 2012 is an “economy, stupid” election. But there is too much detail missing from the Romney-Ryan fiscal plan to give it a clean bill of health. Far from it.

First, the plus points. In selecting Mr Ryan as his running mate, Mr Romney has placed fiscal responsibility at the heart of his campaign. Given that Mr Ryan is the only politician of note to have proposed a drastic cutback to Medicare, the largest and most popular item on the federal budget, his selection took courage. Some believe it was also a reckless attempt to restore the edge to a flagging campaign. Either way, the die is cast. A Romney-Ryan administration would take the axe to public spending and taxes. Mr Obama would not. Mr Romney is offering voters a clear choice.