Sen. Barack Obama's selection of Sen. Joe Biden as his running mate gives Obama immediate foreign-policy gravitas with a dependable party stalwart.
But picking Biden, D-Del., also sends a stark signal that the Obama campaign is worried that the presidential nominee is in danger of flunking the commander-in-chief test.
Rather than helping with the electoral map -- as Sen. Evan Bayh, D-Ind., or Virginia Gov. Tim Kaine might have -- or reinforcing his message of a new brand of leadership, as Kaine or Kansas Gov. Kathleen Sebelius would have, Biden fills a hole on Obama's resume.
They will cut a unique profile as a team: Obama will be the fresh-faced voice of change, eager to stay positive, and Biden will be the experienced yet still energetic inside player, ready to attack when necessary -- and old enough to be Obama's father.
As chairman of the Senate Foreign Relations Committee, Biden is intimately familiar with the international scene and the big national-security challenges that face the nation.
He brings vast experience to a candidate who has spent most of his life outside of the political system.
But the danger for Obama is that he now has a running mate that highlights perhaps his biggest weakness: Sen. John McCain, R-Ariz., enjoys a wide polling advantage on questions of foreign policy and national security, and Biden's selection serves to accentuate those very issues.
And Biden could undercut Obama's core messages.
While Obama issues calls for new leadership and a change in direction, Biden has been in the Senate since Obama was in grade school.
While Obama represents a new face on the national stage, Biden -- after two failed presidential runs of his own -- is a well-known Washington hand.
Republicans will be able to point to statements from Biden himself that call into question Obama's ability to lead.
Biden has said repeatedly that the presidency requires experienced leadership. Referencing Obama, he said at one point that the presidency is "not something that lends itself to on-the-job training."
He sharply questioned Obama's opposition to Iraq war funding during the primaries.
Biden has also earned a well-known reputation for gaffes.
If the first rule of choosing a running mate is to do no harm, Biden is a risky choice: Democratic and Republican insiders are almost unanimous in expecting a handful of clankers from Biden this fall.
Few doubt his political skills.
Biden has a compelling personal story to tell, and will be able to play the attack-dog or policy-wonk role with equal skill. His loyalty and his readiness for the job are beyond question.
Yet for a candidate who speaks in lofty tones about remaking politics, Biden is an earth-bound choice.
With this pick, Obama is signaling not just that he needs help leading, but that he needs help convincing the public that he's ready to lead.