As they watched Joseph R. Biden Jr. step on stage in Springfield, Ill., yesterday, a 65-year-old with white hair jogging to the lectern, many of his longtime friends and colleagues experienced a touch of deja vu: Once again, Biden had resurrected a career that appeared destined for decline.

Nearly eight months ago, Biden withdrew from the 2008 presidential race after winning less than 1 percent of the delegates in Iowa's Democratic caucuses. It was an ignoble failure for one of the most prominent and senior members of the U.S. Senate, and friends worried openly about Biden's psyche. Biden worried only about what he would do next.

That's how it has always been with Biden, Barack Obama's long-awaited choice for vice president. Setbacks are followed by successes, and the cycle repeats. A tragic car accident, brain aneurysms, a plagiarism scandal, two failed presidential runs -- nothing has permanently derailed him.