Joe Biden accepted the Democratic presidential nomination Thursday night, beginning a general-election challenge to President Donald Trump that Democrats have cast as a rescue mission for a country equally besieged by a crippling pandemic and a White House defined by incompetence, racism and abuse of power.

Speaking before a row of flags in his home state of Delaware, Biden urged Americans to have faith that they could "overcome this season of darkness," and pledged that he would seek to bridge the country's political divisions in ways Trump had not.

"The current president has cloaked America in darkness for much too long - too much anger, too much fear, too much division," Biden said. "Here and now, I give you my word: If you entrust me with the presidency, I will draw on the best of us, not the worst. I will be an ally of the light, not the darkness."

Biden's appearance was an emphatic closing argument in a four-day virtual convention in which Democrats presented a broad coalition of women, young people and racial minorities while going to unusual lengths to welcome Republicans and independent voters seeking relief from the tumult of the Trump era.

The former vice president alluded to that outreach, saying that while he is a Democratic candidate, he will be "an American president." And in an implicit contrast with Trump, Biden said he would "work hard for those who didn't support me.""This is not a partisan moment," he said. "This must be an American moment."

The party has offered Biden, 77, less as a traditional partisan standard-bearer than as a comforting national healer, capable of restoring normalcy and calm to the United States and returning its federal government to working order.

He has campaigned as an apostle of personal decency and political conciliation, and as a transitional figure who would take on some of the worst American crises - not just the coronavirus outbreak but also economic inequality, climate change and gun violence - before handing off power to another generation.