Even though Senator Biden comes to the Democratic ticket with decades of political relationships and personal history in electoral battleground states that Senator Obama cannot match, the new team’s advisers acknowledge that Mr. Biden is not a cure-all for the political challenges facing Mr. Obama, of Illinois.

Senator Biden has become widely recognized as a respected voice on foreign policy, the two Iraq wars (against the first, for the second), the Balkans conflict and global AIDS prevention. From his perch as chairman of the Senate Foreign Relations committee, he has aggressively criticized President Bush for his unilateralist approach.

This week was a week of number twos on a variety of fronts. In the US, Joe Biden became Barack Obama’s new sidekick, while in Australia, the minor parties in the Senate geared up to take on their new roles as second fiddles. Meanwhile, in the entertainment world, ‘Stargate Atlantis’ was cancelled and replaced by ‘Stargate Universe’.

Senator Obama, the presumptive Democratic nominee, confirmed that he was picking Biden, a 65-year-old six-term senator from Delaware, early on Friday morning. The choice may be more difficult to swallow for Senator Clinton’s most ardent supporters, especially after it was revealed that she had not even been vetted for the job.

Senator Biden is the chairman of the Senate Foreign Relations Committee, and is familiar with foreign leaders and diplomats around the world. Although he initially voted to authorize the war in Iraq — Senator Obama opposed it from the start — Mr. Biden became a persistent critic of President George W. Bush’s policies in Iraq.

The selection process for Senator Obama’s running mate has been so secretive that most people in his campaign headquarters still did not know what was going on Friday evening. Democrats were not ruling out the possibility that Mr. Obama could surprise the party with a choice other than Senator Biden.

As intense as the anticipation over Barack Obama’s choice is, it pales next to the hubbub over whether John McCain is going to tap Joe Lieberman, who was Al Gore’s running mate in 2000. This would give Lieberman a unique niche in American history — one politician who was the vice-presidential nominee for both parties. We would speak of it with awe, like that story about the two-headed turtle in Brooklyn.

Senator Obama’s advisers said the candidate all but reached his decision while on vacation in Hawaii. They said the nomination process was unexpectedly intense, and was condensed because Mr. Obama did not want to start actively vetting potential running mates before Senator Hillary Rodham Clinton quit the race in June.