WILMINGTON, Del. —  Joe Biden was elected the 46th president of the United States on Saturday and used a victory speech to his supporters to urge Americans and lawmakers of both parties to lay aside the polarization of the last four years and address the grave problems facing the country.

“Let this grim era of demonization in America begin to end here and now,” Biden said as supporters at the drive-in rally in his hometown of Wilmington, Del., honked their car horns in affirmation. “If we can decide not to cooperate, then we can decide to cooperate.”

Hollering into the clear, 50-degree night air, Biden invoked the words that launched Barack Obama’s national political career 16 years ago at the Democrats’ 2004 convention.