That is the real significance of Barack Obama's choice of running mate for this autumn's presidential election: it is the first serious test of the Democratic candidate's judgement. By unveiling Joe Biden as his running mate in Springfield, Illinois, on Saturday, Mr Obama would appear to have passed it.
It is a politically shrewd appointment, of course. The presence on the ticket of Mr Biden, a six-term Senator for Delaware, is intended to reassure those voters who fear that Mr Obama's relative youth makes putting him in the Oval Office something of a gamble. From now on, when Mr Obama's Republican opponent, John McCain, attacks his rival's lack of experience, the Democratic nominee can point to the bulging CV of his veteran running mate.
From the Democrat perspective, Mr Biden has an appealing personal biography, too. Party strategists will be hoping that Mr Biden's humble roots in Scranton, Pennsylvania, will help win over those blue-collar voters in places such as Ohio and Michigan who vastly preferred Hillary Clinton to Mr Obama in the primaries. They also seem to be calculating that Mr Biden's full-blooded political style will complement Mr Obama's somewhat cool and cerebral approach. And Mr Biden's passion and proven political street-fighting abilities might well prove an asset on the campaign trail (providing the Delaware Senator can suppress his unfortunate tendency to shoot from the hip).
We should, however, bear in mind that this is by no means the most radical choice Mr Obama could have made. If he had wanted to make a big splash he might have opted for a woman such as the Kansas Governor, Kathleen Sebelius, or the Hispanic Governor of New Mexico, Bill Richardson. Alternatively, he might have chosen a running mate likely to deliver him support in a key swing state such as Ted Strickland, the Governor of Ohio. Mr Obama's unflashy and essentially pragmatic choice points to a growing maturity and seriousness of intent on his part. It also points to an ability to identify weaknesses in his campaign and do something about them.
A wealth of knowledge
As chair of the Senate Foreign Relations Committee, Mr Biden has accumulated a wealth of knowledge of international affairs and acquired a hefty contacts book of world leaders. This month's Russian military incursion into Georgia is a sobering reminder that such expertise will be needed in the White House in the coming years. It may even be needed by Mr Obama between now and November's election. The appointment of Mr Biden covers a potential gap in the Obama armour.
If there is a drawback, it is the fact that this choice of running mate seems to contradictMr Obama's long-standing campaign theme of shaking up America's creaking political machinery. Mr Obama's argument in Springfield that "for decades, [Mr Biden] has brought change to Washington, but Washington hasn't changed him" is a neat attempt to square the circle, but not a very convincing one. For all his straight-talking charm, Mr Biden is, at heart, an establishment figure.
There is, though, a danger of reading too much significance into Mr Obama's choice. For all the constitutional significance and potential power of the office of vice-president, the identityof the running mate tends to be a negligible influence on the outcome of modern presidential elections. Two names will be on each ticket in November, but Americans tend to vote with the president in mind, rather than the deputy.
Healing the rift
Of much greater significance will be the Democratic Party convention in Denver this week at which Mr Obama will be officially nominated as the candidate. Will the rift between Mr Obama and the still-powerful Clinton camp be fully healed? More importantly will it be seen to be healed by the outside world?
Then another question looms. Will there be momentum for Mr Obama coming out of Denver? Mr McCain is running neck and neck with his opponent in the polls and Mr Obama's campaign has yet to catch fire nationally in the manner in which his team must have hoped it would by now. This is where the race gets truly interesting.
Mr Obama appears to have successfully negotiated one hurdle with this weekend's appointment. But the biggest challenges for the Democratic candidate all lie ahead.
