The truth is, Biden had been smiling for days.
Across the country, voters responded. If Democrats had tasted the revolution Sanders was offering in Iowa, New Hampshire, and Nevada, in states throughout the South they quickly turned away, and back toward the more familiar center-left politics Biden represents.
Buoyed by black voters, the former vice president won early and convincing victories in Virginia, North Carolina, and Alabama. He racked up dozens of delegates in beating Sanders so handily. And even in Vermont, Sanders’s home state, Biden appeared likely to cross the 15 percent threshold needed to pick up some delegates.
He went on to win Minnesota, likely thanks to Klobuchar’s endorsement, and Massachusetts, where he beat not only Sanders but a favorite daughter, Senator Elizabeth Warren.
Source: How Biden Won Super Tuesday – The Atlantic