Biden’s verbal mumbles and occasionally meandering responses in the debate heightened voter concerns that he might not be fit to serve another four-year term. President Joe Biden said on Friday he intended to defeat Republican rival Donald Trump in the November presidential election, giving no sign he would consider dropping out of the race.Biden was speaking after a feeble debate performance that dismayed his fellow Democrats. “I know I’m not a young man, to state the obvious,” an ebullient Biden said at a rally one day after the head-to-head showdown with his Republican rival – a showdown wi…