US Vice Presidential debates rarely matter. Sure they produce some moments that are remembered – who can forget Lloyd Bentsen's memorable put down of Dan Quayle in 1988 when he told him "Senator, you are no Jack Kennedy" - but the first requirement of the number two on the ticket is do no harm.
However a confluence of events suddenly makes the meeting on Thursday of Vice President Joe Biden and his Republican challenger Paul Ryan in Kentucky much more significant.
First there is President Obama's Denver debacle, a truly terrible performance which has begun to haunt him in the polls as well as the press. It allowed the Republicans to pick themselves up off the floor for the first time in weeks and gave the party something to cheer about, which they had been sorely missing.
At Mitt Romney's first major campaign stop after the debate, in Virginia, people sat in traffic lines 10 kilometres long for more than three hours to get to the field where the Republican candidate and his VP pick were due to speak. There was a different air to this rally. It felt like no longer were Republicans turning out because they simply wanted to beat Barack Obama, this was a gathering of people who actually wanted to vote for Mitt Romney.
By default, Biden has been handed the job of picking up the Democrats, dusting them down and giving them fresh hope. Four years ago, against the inexperienced Sarah Palin, he was told to hold back and be aware of the danger of acting like a bully. He delivered what was an acceptable if muted performance. But the 'real' Joe Biden is aggressive and tenacious. He is likely to invoke the phrase he has used repeatedly throughout the campaign to sum up the last four years: 'Osama Bin Laden is dead and General Motors is alive.' And he is more likely to go after Republican vulnerabilities given Barack Obama's failure to do so in Denver. The Democrats have reportedly been studying the transcript from Denver to look for lost opportunities that can be exploited this time around.
Hostility from the left
Biden's opponent, Paul Ryan, is an experienced Washington hand who already polarises the public. The political right wing love him for his policies and proposals, from the scrapping of the guaranteed state pension – or social security as it's known here (something he's walked away from in recent years) - to the radical reorganisation of the national health insurance scheme for seniors – Medicare. For the same reasons he is viewed with deep suspicion if not downright hostility by the left.
The Republicans have begun the predictable game of talking down expectations of their candidate, pointing out that while he has tangled with Democrats on the floor of Congress, he has never appeared in a nationwide televised debate which could attract an audience of up to 40 million. And he is up against someone who has spent 36 years in the senate and made at least two runs for the presidential nomination and hasn't ruled out another run in 2016.
We can expect, in Paul Ryan's own words, Biden to go after him like a 'cannonball' from the first minute. Ryan will also be under pressure because of Mitt Romney's own performance.
He has to explain some of the details of the Republican plans, what government programmes they'd cut to trim the deficit and how they are going to pay for promised tax cuts. He'll also have to deflect the attacks which will undoubtedly come his way. Biden – who has a reputation as a 'gaffe machine' – has to deliver a performance substantially better than that of his boss without creating a controversy which will take the headlines for days.
People still vote for the top of the ticket, but the outcome here will shape the coverage of the race over the next few days. Both sides need a win, so what is normally a sideshow is now much more important.