Biden will soon face his second Republican vice-presidential candidate. He can expect more of a challenge than last time
For the second time, vice-president Joe Biden will face off against a Republican opponent on the bottom half of a presidential ticket.
Though Paul Ryan may not appear as strikingly different from Biden as Alaska governor Sarah Palin was in 2008, the firebrand Wisconsin congressman is a formidable and contrasting opponent.
Here are some of the key points of difference between the two vice-presidential candidates.
Age
Joe Biden is no spring chicken. He was born in 1942 as the second world war raged in Europe and Asia. He is now silver-haired and 69 years old, none of which is unusual in Washington DC, especially in the Senate where Biden spent so much time.
Ryan, however, is a self-titled Republican 'young gun'.
Just 42 years old, he was born in 1970: the first ever person on a presidential ticket from the "Me Decade". He is also a fitness fanatic and avid hunter.
Experience
Ryan may come across as a youthful breath of fresh political air compared to Biden, but there is the question of experience to consider.
Biden has been at the heart of American power for four years already as the incumbent vice-president.
Before that he spent long years in the Senate, first being elected in 1970 when he was just 30.
He became a specialist in foreign policy, frequently travelling abroad and involving himself in often bitter foreign conflicts, something he has continued as vice-president.
Ryan, however, has little practical experience outside Washington.
Biden also had a career as a lawyer before he became a politician. Ryan basically went straight to Washington. He also has focused almost entirely on domestic policy issues. That lack of foreign experience was a notorious weakness for Palin.
Debating skills
Ryan is no slouch when it comes to debating. He is a confident speaker and, as a budget specialist, he has a mastery of facts and figures at his fingertips.
He is, in short, about as far from Sarah Palin as you can get. Biden on the other hand is a successful politician, fluent and passionate.
But he is also well known for making verbal gaffes and has a tendency – like many senators – to speak for far too long.
In a famous exchange in Baltimore in 2011, Ryan had a brief public debate with President Barack Obama over fiscal issues.
Ryan held his own and it made him a conservative hero. Biden just about beat Palin in 2004 in their face-off (and some would even debate that, saying Palin did better).
Ryan will be a very different proposition.
Background
Neither man has quite the compelling story of a personal journey of President Barack Obama. Or the colourful wonder of a Sarah Palin (a moose-hunting beauty queen turned state governor and mom of five).
Ryan's background is solidly middle class and midwestern. He does not have Mitt Romney's wealth and privilege, instead hailing from a small city in Oklahoma. Biden's background is a little more blue collar.
He was born in Scranton, Pennsylvania, and had a slightly more hardscrabble life than Ryan as his father went through a period of struggling for work.
But neither man can claim to have been born to true poverty in the way that, say, Democratic Senate leader Harry Reid can.
Religion
Both men are Roman Catholics, so religion, at least, is likely to be an area of common ground and not something for too much debate (unlike Palin whose evangelical beliefs attracted a lot of unfavourable media attention).
However, Ryan is staunchly anti-abortion whereas Biden is pro-choice.