MILWAUKEE — The Democratic primary race began as a clash of ideas. But when the Democratic National Convention convened on Monday, the party assembled with a singular aim: defeating President Trump.
From the progressive left to the moderate wing, Mr. Trump has served for months as the glue keeping the party from fracturing. And never has this détente been more obvious than in the wide-ranging lineup for the first night of the convention, when, in the name of unity, the virtual stage was open not just to Democrats of various persuasions but to Republicans as well.
The festivities conveyed one message from the Democrats. Whatever their ideological differences with one another or the Democratic nominee Joseph R. Biden Jr., ousting Mr. Trump was the primary concern.
“We have got to vote for Joe Biden like our lives depend on it,” said Michelle Obama, the former first lady.
The appeal came from other political leaders including John Kasich, a onetime Republican candidate for president; Senator Bernie Sanders, the progressive standard-bearer; and also Democratic moderates including Senator Amy Klobuchar of Minnesota, Gov. Andrew M. Cuomo of New York and Gov. Gretchen Whitmer of Michigan.
From the opening moments, which featured a dramatic recitation of the preamble to the Constitution and a mosaic of young people from across all the states and territories singing the national anthem, the convention was a surreal projection of America, slickly produced for a television audience no one could see. The event repeatedly touched on themes that have galvanized voters in recent months — racial justice, the coronavirus crisis, the mail — and portrayed the Democratic Party as uniquely able to heal a scarred nation.
The speakers made clear that unity does not mean total agreement. Mr. Sanders and Mr. Kasich were both explicit in saying that they disagree with Mr. Biden on some matters, but are behind him nonetheless.
“I’m a lifelong Republican, but that attachment holds second place to my responsibility to my country,” Mr. Kasich said.
Taken together, the spectacle was a fitting coda to a primary season defined by the notion of electability. More than policy or identity, it had been this all-consuming desire to beat Mr. Trump that cut across ideological and generational lines. The global pandemic and Mr. Trump’s handling of it has only intensified the resolve.
On a night that featured video testimonials from many Americans who might not normally be on a political convention stage, Kristin Urquiza, spoke to the coronavirus crisis directly: She blamed Mr. Trump for the death of her father — a Trump supporter — to Covid-19.
“One of the last things that my father said to me was that he felt betrayed by the likes of Donald Trump,” she said. “And so when I cast my vote for Joe Biden, I will do it for my dad.”
It was an arresting moment, and one that reinforced the urgency the party hoped to impart.
The Democrats’ unified front is a striking departure from four years ago, when Sanders supporters booed and jeered at Hillary Clinton, then the party’s nominee. Days before the convention, the release of stolen Democratic National Committee emails revealing that party officials had been eager to help Mrs. Clinton and undercut Mr. Sanders confirmed longstanding complaints of bias from the Vermont senator and threatened to plunge the proceedings into chaos.
But if the convention is intended to rally Democrats with a common resolve, it is also a reflection of an essential quality of Mr. Biden’s, harking back to his days in the Senate: He strives to build bipartisan consensus and believes compromise across political divides is possible. Since winning the primary, he has stamped this political worldview onto the party’s DNA. The result is a convention that is more an extended infomercial built to persuade the skeptical moderate than a rousing show of defiance meant to fire up the party’s base.
Standing at a literal cross in the road, Mr. Kasich made this point explicit: pitching Mr. Biden as a moderate and assuring Republicans and independents that he would not tack too far left. “No one pushes Joe around,” he said.
There are still serious reservations about Mr. Biden among progressives, who have already signaled that they intend to push Mr. Biden should he be elected, on issues including health care, climate change, education and criminal justice. Some have refused to back the Democratic Party platform because it does not support “Medicare for all,” a symbolic move that nevertheless suggests conflict to come.
For now, those ideological fights could wait.
The shared, Trump-induced incentives created a rare mind meld between members of the Democrats’ left wing and Republicans.
“This isn’t about a Republican or Democrat,” said Christine Whitman, the former New Jersey Governor and a Republican, “it’s about a person.”
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Mr. Sanders offered voters a similar message — that the election was also about reducing harm and removing Mr. Trump in a time of crisis. He laid out the ways Mr. Biden’s policy agenda would make progress, but he also stressed that any policy differences were not worth sitting out the election.
“To those who may have voted for Donald Trump in the last election: The future of our democracy is at stake. The future of our economy is at stake. The future of our planet is at stake,” Mr. Sanders said. “My friends, the price of failure is just too great to imagine.”
Mr. Sanders once again addressed a Democratic convention as a runner-up, but the context was far different than it was last time, when his sustained attacks on Mrs. Clinton helped foment deep divisions between his wing of the party and establishment Democrats that burst out into the open on the convention floor.
During his 2020 presidential bid he made clear that beating Mr. Trump was a top priority, placing it on a par with his calls for progressive policies like “Medicare for all” and tuition-free public college. In the interest of unity, he vowed to support the eventual nominee if it wasn’t him.
On Monday, he ticked off examples “of how Joe will move us forward,” including Mr. Biden’s support for a $15 minimum wage. And though he acknowledged he and Mr. Biden did not agree on health care, he allowed that Mr. Biden had “a plan that will greatly expand health care and cut the cost of prescription drugs.”
Rarely has Mr. Sanders spoken so charitably about a moderate former rival.
Mrs. Obama, who delivered the final speech of the night, did not focus on policy specifics. Instead, the former first lady repurposed her 2016 mantra, “when they go low, we go high,” saying that she believes in that value more than ever, even after four years of Mr. Trump.
“Going high is the only thing that works, because when we go low — when we use those same tactics of degrading and dehumanizing others — we just become part of the ugly noise that’s drowning out everything else,” she said.
In some ways, the message of the Democrats’ first night of virtual programming was more indicative of the 2018 midterm elections, during which moderate victories existed alongside progressive gains, and the Democratic Party swept to power with a big-tent message of holding Mr. Trump’s administration accountable.
Matt Bennett, co-founder of the center-left political group Third Way, said it was vital for Democrats to give Mr. Biden space to make overt appeals to conservative and moderate voters.
“Anytime you’re expanding the size of the tent, that’s helpful,” Mr. Bennett said. “There are not a lot of persuadable voters late, but to the extent there are any, you have to give them permission to do what they know is right.”
Mr. Biden has, in recent polling, exploded to an early lead against Mr. Trump behind a unique coalition that includes seniors who have soured on Mr. Trump after his handling of the coronavirus pandemic, college-educated moderates in suburbs, and white voters without a college degree. A portion of the programming was laser targeted at those constituencies.
The night showcased not just Mr. Biden’s pitch for November, but also the themes that have grounded his political career. A longtime senator from Delaware, he was known for his relationships with both Republicans and Democrats, and leaned on those personal connections to pass legislation throughout his career.
His political history has not come without criticism, and Mr. Biden continues to be accused by more liberal members of his party of caring more about Washington traditionalism than ideals like social justice and equality. Indeed, it was the thrust of the attack that Senator Kamala Harris, whom Mr. Biden chose as his running mate last week, lobbed at him during their first presidential debate.
It remains a sticking point. Representative Alexandria Ocasio-Cortez, a leader of the progressive wing of the party who will speak at the convention Tuesday, tweeted her displeasure at Mr. Kasich’s speaking slot, considering his anti-abortion views.
“It’s great that Kasich has woken up and realized the importance of supporting a Biden-Harris ticket. I hope he gets through to GOP voters,” Ms. Ocasio-Cortez said. “Yet also, something tells me a Republican who fights against women’s rights doesn’t get to say who is or isn’t representative of the Dem party.”
With a different nominee, in a different time, such pressure from the left wing of the party might worry Mr. Biden’s campaign. But this is Mr. Biden, consensus builder at heart. And the opponent is Mr. Trump, the great Democratic uniter.
Cori Bush, the progressive St. Louis activist who recently won her Democratic primary and is most likely headed to Congress next year, said the priorities for Democrats were driven by their constituents: “The people in our community want Donald Trump out.”