US President Joe Biden has made a forceful bid to quell anxieties over his unsteady showing in his debate with former President Donald Trump. Biden’s halting delivery and meandering comments, particularly early in the debate, have fuelled concerns among members of his own party that at 81 he’s not up for the task of leading the country for another four years. “I know I’m not a young man. State the obvious,” he told supporters at a rally in North Carolina. “I don’t walk as easily as I used to. I don’t speak as smoothly as I used to. I don’t debate as well as I used to. But I know what I do know…