WASHINGTON — It may have taken a once-in-a-century pandemic, but the Democrats are not in disarray.

After presidential primary races in 2008 and 2016 that stretched across all 50 states, the 2020 contest ended on an altogether tidy note on Monday as Senator Bernie Sanders appeared on a live stream with Joseph R. Biden Jr. and told him: “We need you in the White House.”

The endorsement was quick in the making, full-throated in nature and offered a vivid illustration of how differently this election is unfolding from the often bitter last two Democratic nominating contests.

“The way Bernie did this was really helpful,” said former Gov. Howard Dean of Vermont. “There is clearly no animosity between the two of them and this will definitely make it easier for Bernie’s supporters to vote for Biden.”

Among those Sanders voters are thousands of young people who are not old enough to remember a Democratic primary that concluded so quickly and quietly. Many of the Generation Z and millennial progressives going to the polls this fall grew up on ideological fights and policy debates that lasted until everyone had a chance to vote in the primaries.