Joseph Robinette Biden Jr. was sworn in Wednesday as the 46th president of the United States, rising to the pinnacle of a career in public leadership that began a half century ago and now forces him to confront convulsing challenges dividing a fractured nation.

With his hand on his family Bible, Biden recited the oath taken by his predecessors, promising to “faithfully execute the office of president of the United States,” and, with the help of God, “preserve, protect and defend the Constitution of the United States.”

Moments before, Kamala D. Harris took her oath of office, making her the country’s first female vice president, and also the first Black American and first with Indian heritage to hold the second highest office in the land. She had placed her hand on twin Bibles, one from a family friend and the second belonging to Thurgood Marshall, the first African American justice of the Supreme Court.