Tradition holds that the vice-president of the United States matters about as much as an anonymous body double in an all-star movie.
John "Cactus Jack" Garner, Franklin Roosevelt's deputy, supposedly remarked that the job was "not worth a bucket of warm spit". The fluid he actually mentioned was not saliva.
Modern commentators are no less scornful. The satirist Jon Stewart rarely misses a chance to ridicule Joe Biden as a blowhard, despite the fact that Barack Obama's understudy was re-elected to the Senate on six occasions. In Armando Iannucci's Veep, the Americanised version of The Thick of It, a running gag sees vice- president Julia Louis-Dreyfus asking her secretary repeatedly if the president has called. He never calls.
It's mildly funny, but not even half the story. While few mention FDR and Cactus Jack in the same breath, and most only remember Dan Quayle for his inability to spell potato while trapped in the shadow of the elder George Bush, the vice-presidency is more than a comedy walk-on part.
Lyndon Johnson altered America and the world in the 1960s after the murder of John Kennedy. Dick Cheney, it sometimes seemed, did more to shape White House policy while Bush the younger was supposed to be in charge than any other individual, the president included.
The occupant of Number One Observatory Circle is, famously, only a heartbeat away from the Oval Office: the 25th amendment is clear about that. But the non-job matters too because these days it comes with a near-explicit contract. For 60 years, time and again, vice-presidents have regarded an eventual run at the presidency as their right and reward. The results have been mixed, but the pattern is established.
Paul Ryan is not just making up the numbers in Mitt Romney's presidential campaign, therefore. Nor, in a contest that is turning out to be closer than many Democrats and most Europeans expected, has this radical conservative – the euphemism will do – been chosen for his self-effacing manner. By selecting Mr Ryan as his running mate, Mr Romney is delivering a statement. By accepting the role, the 42-year-old foe of big government and liberals is staking a claim on the presidency in four or eight years' time.
The world might want to think about that. Mr Romney has altered his positions so often he could drive a sat-nav to hysterics. Mr Ryan is a child of the American conservative revolution who sees no point in compromise. The Tea Party faction love him; the deficit obsessives adore him. For social conservatives he ticks every box and appends a few unpleasant checklists of his own.
Mr Ryan is one measure of what the Republican party has become. He doesn't just like guns; he wants "concealed carry" laws extended across the entire country. He doesn't just oppose abortion; he wants to criminalise the procedure, even in cases involving rape or incest. Mr Ryan wants a constitutional ban on same-sex marriage, the privatisation of social security, tax cuts for the top 2% and spending cuts, lots of spending cuts, for everyone else save the military. He rejoices in intolerance.
This Republican opposed Mr Obama's health care reforms, predictably, but also voted against equal pay legislation affecting women and a bill of rights for credit card holders. Attempts to reform Wall Street and better protect American consumers have meanwhile aroused his indignation. In essence, his programme for government involves the destruction of government. Like all his kind, he is contemptuous of the world and the world's opinion.
We have already had one taste of that. As a proud defender of the planet's most expensive and unjust health care system, Mr Ryan had barely launched his vice-presidential campaign on Saturday before he was attacking the NHS as an obstacle to self-reliance and – the greater crime – tax cuts for the better off. This is a candidate who believes that David Cameron's Coalition is socialism in action.
Mr Ryan is no-one's fool, however. In conservative circles, in fact, he is regarded as something of an intellectual, the type who will not merely reject Mr Obama's budget proposals but attempt to rebut them. Nor, unlike Sarah Palin, is he a novelty right-winger chosen for his appeal to the fabled "base". His appeal is real, but so is his experience as a congressman of 13 years. Mr Ryan started early. He is now ideally placed to succeed or supplant this year's candidate.
The Obama campaign would like to believe that he is too extreme even for "middle" America. That might be wishful thinking. Millions of dollars have been flooding in to Mr Romney's campaign since the weekend; crowds, reportedly, are enthused. The Republicans who distrusted the prevaricating Mormon have been reassured by an authentic, hard-line zealot.
What about the rest? Fans of Mr Obama, not least in Europe, have a few inconvenient facts to consider. First, the contest was close even before Mr Ryan made his appearance. The Real Clear Politics poll average as of Sunday night gave the President a lead of only 4.7%; one CBS/New York Times survey in mid-July even put Mr Romney ahead. Numerous other tests of opinion have left the difference between the candidates well within the margin of error.
Equally, disillusionment with Mr Obama is widespread. There might be real fear of the Republican alternative when unemployment is high and the economic recovery is fragile. But a Democrat appeal to "hope" won't work again. Too often, it has turned out to be a false prospectus.
Finally, there is the fact of Mr Ryan himself. He is a plausible candidate because American politics, feral and furious, has all but ceased to resemble its European counterpart. Mr Obama has not even begun to halt his country's relentless drift to the right. The embrace of guns, God, tax cuts and isolationism is no longer freakish. For many it is, and always was, the American way.
Announcing his running mate in Norfolk, Virginia, on Saturday, Mr Romney made a typically clumsy slip by asking the crowd to welcome Mr Ryan as "the next President of the United States". Many believe that's exactly what he is. Rupert Murdoch, should he be your guide, declares that the vice-presidential candidate is "almost perfect".
If you thought Mr Bush was bad, prepare to think again.
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