Sustaining energy through four days of a political convention is never easy. It's even more challenging during this, the first virtual convention. On the second night of the Democratic National Convention, party leaders tried to blend its past with its future.

Key takeaways from night two.

DEMOCRATS DISPLAY BIG TENT

Joe Biden, who was formally nominated Tuesday night in a virtual roll call of states, doesn't shy away from the obvious: He's a 77-year-old white man leading a party that celebrates its racial and ethnic diversity and gets a majority of its votes from women.

He has at times offered himself as a bridge to bring together that coalition, calling himself a "transitional figure" for the party and the country.

Democrats tried to put that on vivid display, an ideological arc that spanned the New Democrat centrism of former President Bill Clinton to the new century progressive movement of Rep. Alexandria Ocasio Cortez, who was born in 1989, the year after Biden's first presidential run.

Democrats were trying to show that their party tolerates differences in ways that the Republican Party led by President Donald Trump does not. The Democrats honored Clinton, and former president Jimmy Carter, along with the party's nominee in 2004, former Secretary of State John Kerry. Cindy McCain, whose husband, John, was the Republican nominee in 2008, appeared in a video praising Biden.

Former President George W. Bush, the only living GOP ex-president, and Sen. Mitt Romney, the party's nominee in 2012, will not be part of the Republican convention next week.

In a 17-person keynote address that was part relay, part reminder of the party's blended constituencies, followed by a roll call of the states, the ethnic and racial contrast with Republicans is obvious. For Democrats, that was the point.

PUNCHES LANDED, NOT PULLED

Donald Trump's journey to the presidency began with then-President Barack Obama mocking the reality TV star relentlessly during the White House correspondents' dinner in 2011 — a brutal ribbing that propelled the notoriously sensitive mogul toward his 2016 run.

But nobody's making jokes now. During the first two days of the Democratic National Convention, the party's luminaries — and even some Republicans — have grimly warned the public that he represents a fundamental danger to democracy.

"He treats our country like it's his family business," warned former Assistant Attorney General Sally Yates. "America, Donald Trump has quit on you," Senate Minority Leader Chuck Schumer said. "He won't defend our country, he doesn't know how to defend our troops. The only person he's interested in defending is himself," said former Secretary of State John Kerry.

Michelle Obama and Bill Clinton also devoted chunks of their speeches to warning that the president is a fundamental threat to the country.

Usually conventions feature stinging put-downs of the rival standard-bearer and the occasional lacerating speech. But the 2020 Democratic convention is notable for the consistency of dire warnings about the other party's leader.

KEYNOTE BY COMMITTEE

Conventions usually follow a standard ritual. But it's not surprising that a virtual convention would change that.

Biden's campaign used the moment not to anoint a single emerging party star, but rather 17 of them, reflecting the diversity of race, age, geography and identity.

It was a stunt for sure, with selfies, ring lights and tightly scripted hits on Trump. But it also seemed effective to make the point, that Biden wants to provide a gateway for young leaders.

"A new generation of leaders is rising up," said Pennsylvania state Rep. Malcolm Kenyatta, an openly gay lawmaker who praised Biden for supporting marriage equality earlier than many older politicians.

Kenyatta and 15 other speakers led up to Stacey Abrams, the 46-year-old Georgian who in 2018 narrowly missed becoming the first Black woman elected governor of a U.S. state. Abrams also was among the 11 women that Biden interviewed as finalists for his running mate.

The keynote was bookended by a lineup of the Democratic old guard, led by Kerry and two former presidents, Clinton and Carter.

Biden has made clear he's casting a wide net in November. The convention's first night was mostly showcasing ideological diversity. The keynote and the rest of Tuesday showcased what Biden hopes is generational diversity in his coalition.

ROLL CALL: DIFFERENT, BETTER

As much as any segment, the roll call to nominate Joe Biden officially highlighted the difference between a traditional convention and a virtual one. And this change seemed to represent an improvement.

Rather than hopscotch across a convention floor, the roll call hopscotched across the country and overseas, with delegates celebrating their home states and territories and making plenty of pitches for Biden. (They still had those placards with the delegation names.)

Alabama's votes were cast from the Edmund Pettus Bridge, site of the 1965 voting rights marches and Bloody Sunday. Utah highlighted its statewide mail voting and 80% voter turnout. Iowa's presentation, set in a cornfield, noted the state's recent storm devastation. Pennsylvania cast its votes in front of Biden's boyhood home in Scranton.

The ending featured a live shot of Biden, with his family, thanking delegates "from the bottom of my heart." Awkward in spots, but a more engaging approach than the usual.

CLINTON, BRIEF FOR ONCE, HAMMERS TRUMP

Bill Clinton has now spoken at 11 Democratic national conventions. But he's never had a more tentative grasp on the party, or a tighter window, than he had Tuesday.

That Clinton was speaking at all was mildly surprising given how his sexual dalliances appear to some in the post-MeToo era. But the notoriously prolix president — whose 2012 speech for Barack Obama ran nearly 50 minutes — was kept to five minutes during the tight, all-online convention. And he wasted no time scorching the man who defeated his wife in the 2016 election.

"If you want a president who spends his day watching hours of TV or zapping people on social media, he's your man," Clinton said of Trump in his prerecorded speech. He slammed Trump for making the Oval Office "the storm center" rather than "the command center" during the pandemic, and for the nation's dismal track record fighting the disease.

For once, Clinton showed that less was more.

JILL BIDEN'S AUDITION

Speaking from a classroom at Brandywine High School in Wilmington, Delaware, where she once taught, Jill Biden juggled several jobs Monday: tell her own story, humanize her husband and validate him as a would-be president.

And it came with a big spotlight.

"I know that if we entrust this nation to Joe, he will do for your family what he did for ours — bring us together and make us whole," she said. "His faith is unshakable," she added.

Jill Biden talked of her own career as an educator — she continued to teach college full-time as the vice president's wife. And she told of how she struggled after the Bidens' son Beau died during Joe Biden's second term as vice president. "I wondered if I would ever smile and feel joy again," she said, but she noted that her husband "went back to work" amid his own grief.

Jill Biden may not have the presence that Michelle Obama brought to the screen Monday. She won't run for president herself, like Hillary Clinton. But she's proven herself a skilled, adept defender of her husband.

On this night, she also let Americans take a measure of her.