The American people will decide whether by adding Congressman Paul Ryan to his ticket, Mitt Romney, the Republican candidate for president, has become more likely to prevail against president Barack Obama in November. What is clear is that Mr Romney’s bold choice for the vice-presidential slot will focus the campaign on the issues that US voters need to debate.

Mr Romney has long struggled to convince voters about what he stands for. Some of his record as governor is difficult to square with attacks on Mr Obama, whose healthcare law resembles the statewide health programme introduced by Mr Romney in Massachusetts. In the Republican primaries, Tea Party supporters who never accepted Mr Romney as a true believer in their principles, often called for “anyone but Romney”.

Mr Ryan, in contrast, is anything but undefined. He is a conservative of the libertarian kind, who comes across as deeply committed to much smaller government. He may be able to energise the Republican-leaning voters who have remained cool on Mr Romney. For a challenger’s campaign that remains on the defensive against the White House, this is a shrewd choice.