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.
Not since 2004 has the Democratic Party rallied behind its nominee this early. That year, when a Republican incumbent was also in the White House, Mr. Dean, John F. Kerry and a handful of other Democrats competed through just seven weeks of primaries and caucuses before Mr. Kerry stood alone and triumphant.
And for the first time in 16 years, it appears that there will be no drama ahead of the convention, no protracted negotiations over personnel, policy or even endorsement stagecraft.
The moment demands sobriety and Mr. Sanders recognized that.
“The threat is so profound,” said Paul Begala, the longtime Democratic strategist, alluding to both the coronavirus and what Democrats see as the risk if President Trump wins re-election. “There’s just no space for the normal gamesmanship that may have played out.”
Mr. Biden was already on his way to claiming the nomination before the country effectively shut down to combat the pandemic. But the virus all but ended the race, monopolizing the attention of voters and leaving Mr. Sanders no opportunity to forge ahead with even a symbolic bid.
The deadly outbreak also seemed to accomplish the impossible — intensifying the already immense Democratic fear of a second Trump term, which had been the most animating issue of the primary all along.
Still, for a movement figure like Mr. Sanders, enough of an independent that he still refuses to formally join the party whose nomination he nearly claimed in 2016, it was a remarkable moment of “self-sacrifice,” as Mr. Begala put it.
It was also a moment that plenty of establishment-aligned Democrats were skeptical would ever happen.
The working assumption among many in the party had been that Mr. Sanders would again compete in every state and take his candidacy to the convention.
But unlike in 2016, when few Democrats or Republicans believed Mr. Trump could win, there’s little doubt now that the president could be re-elected.
“We’ve got to make Trump a one-term president,” Mr. Sanders said in the video, alluding to the president’s handling of the virus. “I will do all that I can to make that happen.”
Such talk has left Democrats with an unusual sensation — the feeling of unity in springtime. Hoping to second, and third, that emotion, Mr. Biden’s campaign was rolling out Democratic luminaries this week whose support of the nominee was expected: former President Barack Obama, Senator Elizabeth Warren and, likely to come, the 2016 nominee Hillary Clinton.
The rapid rallying recalls the 2004 race, when the country was also in a mood of alarm, over the war in Iraq and the threat of terrorism.
Still, for a famously fractious party, this quick turn toward unity — it was just six weeks ago that Senator Amy Klobuchar and Pete Buttigieg got things rolling by endorsing Mr. Biden — is out of the norm.
After all, there are still Democrats who consider themselves Carter people or Kennedy people, depending on whether they were aligned with former President Jimmy Carter or Senator Edward M. Kennedy in the 1980 primary.
“Of all the unpredictable events in the 2020 campaign cycle, from Biden becoming the nominee to campaign events being shut down, the primary being wrapped up in April is right up there,” said Jennifer R. Psaki, who worked on former Mr. Obama’s 2008 campaign.
It’s easy for all but the most dedicated political junkies to forget, but the last two Democratic races were not just contentious — they also ended on sour notes.
Mrs. Clinton, still campaigning hard against Mr. Obama in late May of 2008, mused about how uncertain the race was, indelicately recalling that Robert F. Kennedy was assassinated in June of the year he ran. That was before a summer leak that Mr. Obama had not even vetted Mrs. Clinton to be his running mate. And remember the PUMAs? That group of Clinton die-hards — the acronym stood for Party Unity My Ass — threatened not to support Mr. Obama in the general election.
The tensions all added up to very little in the fall, particularly once the economy cratered and the general election between Mr. Obama and Senator John McCain became less than competitive.
Party unity wasn’t enough for Mr. Kerry in 2004, of course — he lost to President Bush in the fall.
But in a competitive race, binding up the wounds from the primary can prove pivotal.
That certainly didn’t happen four years ago after the long nomination battle between Mr. Sanders and Mrs. Clinton.
Sanders supporters booed leading Democratic officials at the 2016 convention, which began just as their national party chair was forced out because a cache of hacked emails showed the committee working to undermine Mr. Sanders’s campaign. And even though Mr. Sanders offered his support for Mrs. Clinton, and campaigned for her in the fall, there was never the sort of rapprochement that he and Mr. Biden displayed on Monday.
That mutual distrust mattered.
Studies have shown that the number of Sanders supporters who defected to Mr. Trump in 2016 was not significantly higher than the typical crossover voters who defect to the other party in the general election. But enough of them in the most crucial states backed Mr. Trump or a third-party candidate to swing the election away from Mrs. Clinton.
And if this fall’s election is anywhere near as competitive as 2016, when less than 80,000 voters across three Rust Belt states determined the presidency, Mr. Sanders’s fast and full embrace of Mr. Biden could prove decisive.