Presumptive President-elect Joseph R. Biden said Saturday evening that he plans to be a president for all Americans and that he’ll hit the ground running to try to “heal” the country as he claimed a mandate from the American people to govern cooperatively and reach across the aisle. Mr. Biden spoke after multiple news outlets declared him the winner of the 2020 presidential election late Saturday morning, four days after Election Day on Tuesday. “The people of the nation have spoken. They’ve delivered us a clear victory,” Mr. Biden said. “I am humbled by the trust and confidence you placed...