Biden 'never more optimistic' on campaign in Philadelphia

President Joe Biden expressed optimism on the future of the United States on Sunday as he continued campaigning for a second term in office in the face of calls for him to step aside on health grounds.

"I honest to God have never more optimistic about America's future. If we stick together, I really mean it," Biden said in an historic church in Philadelphia whose congregation is largely black.

Biden was given an enthusiastic reception, reading his address to the congregation in a powerful voice and not deviating from the script.

He noted that he was hosting a NATO summit in Washington next week. "The world is looking at us, no joke. The world is looking to America ­ not to carry the burden but to lead their hopes," he said.

Biden's television interview on Friday did little to dispel doubts about his fitness to carry out his presidential duties for a further four years. But he insisted that "only the Almighty" could make him drop out of the race.