Absent the routine large crowds and with snow flurries helping to push the tens of thousands of American flags that blanketed the National Mall in the District, President Joe Biden and Vice President Kamala Harris each took the oath of office before an enthusiastic gathering that featured more law enforcement than spectators.

After Chief Justice John Roberts swore him in, the new president spoke about the importance of a unified America after four years of an administration that orchestrated perhaps the most profound divide in modern history.

"My whole soul is in this," Biden pledged. "To o...