 Throughout this election campaign, the 81-year-old president has faced consistent questions about whether he's too old for another four years on the job. On the debate stage here in Atlanta, Mr. Biden's performance was marked by repeated stumbles and awkward moments of silence. Afterwards, there was a heightened level of concern about his fitness for office. The president's outing was so rough that Democrats are publicly and privately questioning whether he should be the party's presidential nominee. Greg Clugston, Atlanta.