Analysis by Maeve Reston, CNN/StyleMagazine.com Newswire

When Kamala Harris appeared with Joe Biden on Wednesday as his running mate for the first time, she showed why he had chosen her.

Gliding past President Donald Trump's sexist depictions of her as "mean" and "nasty," the senator from California shredded Trump's White House record with the agility that comes from her years as a courtroom prosecutor. Yet she delivered those critiques with bright notes of hope and optimism -- accentuated by the smiles that are expected from female politicians.

"The President's mismanagement of the pandemic has plunged us into the worst economic crisis since the Great Depression, and we're experiencing a moral reckoning with racism and systemic injustice that has brought a new coalition of conscience to the streets of our country demanding change," Harris said at the afternoon event in Wilmington, Delaware.

"America is crying out for leadership. Yet we have a President who cares more about himself than the people who elected him," said Harris, who abandoned her own bid for the White House less than a year ago before a single vote was cast. "As someone who has presented my fair share of arguments in court, the case against Donald Trump and Mike Pence is open and shut."

It was a first performance that showcased Harris' political deftness and why she will be a formidable adversary for Trump and Vice President Mike Pence this fall, both in her ability to connect with stories of average Americans struggling through the pandemic and to throw a clean punch without fear of the ramifications.

In her speech, she made a direct contrast between Trump -- who recently shrugged off the more than 165,000 American Covid-19 deaths by saying, "It is what it is" -- and what she described as Biden's qualities of "empathy, his compassion, his sense of duty," adding that she and the former vice president were both "cut from the same cloth."

She charged that Trump's failure to take the virus seriously, to get coronavirus testing up and running, to offer a national strategy for ending the pandemic has led to 16 million people without jobs, "a crisis of poverty, of homelessness" that is "afflicting Black, brown, and indigenous people the most" and "more than 165,000 lives cut short, many with loved ones who never got the chance to say goodbye."

"It didn't have to be this way," she said.

Harris also sought to convey an understanding of what average families are dealing with by pointing to the "complete chaos" over when and how to open schools: "Mothers and fathers are confused, uncertain and angry about child care and the safety of their kids at schools -- whether they'll be in danger if they go or fall behind if they don't."

She eviscerated Trump's leadership failures by noting that his family's wealth had paved his way to power, charging that he had "inherited the longest economic expansion in history" from the Obama administration "and then, like everything else he inherited, he ran it straight into the ground."

Over her career in politics -- as district attorney of San Francisco, California's attorney general, the state's junior senator and now as a presidential candidate -- Harris has sometimes struggled to hold the energy of a room or to sustain the cheers that are so important in maintaining a candidate's momentum.

But in the era of campaigning mid-pandemic, that was not an issue Wednesday in the nearly empty gym, where only socially distant -- and silent -- reporters and staff served as the audience.

Instead, Harris was able to speak directly to the camera in a setting that seemed almost intimate because there were no cheers, applause or distractions -- making her case for why a Democratic win in November might matter in the daily lives of Americans.

She wove aspects of her personal story with Biden's, noting that she had come to know the former vice president because of her friendship with his son Beau, a former Delaware attorney general who died of brain cancer.

Demonstrating the role she will play in humanizing Biden, she touched on the story of how the elder Biden "rode the rails" between Washington and his home in Delaware for four hours a day after his first wife and his daughter died in a car accident so that he would be able to make breakfast for his sons in the morning and tuck them in at night.

"All of this so two little boys, who'd just lost their mom and sister in a tragic accident, would know the world was still turning," Harris said. "And that's how I came to know Joe. He's someone whose first response, when things get tough, is never to think about himself, but to take care of everybody else."

Introducing his running mate earlier in the event, Biden explained why he had chosen Harris, the first Black woman and first person of South Asian descent on a major party's presidential ticket.

As the child of immigrants from Jamaica and India, Harris "knows personally how immigrant families enrich our country," Biden said, adding that "her story is America's story."

Previewing arguments that will be important in key swing states as his campaign tries to convince Americans than they are not better off than they were four years ago, he also tried to link Harris' agenda to his own, noting her efforts to help working families after the foreclosure crisis, when she took on the big banks, and her advocacy for "folks" who are looking for a "fair shot of making it."

Biden seemed to enjoy drawing attention to Trump's sexist remarks about Harris, such as when the President repeatedly called her "nasty" shortly after Biden announced her as his running mate, stating that the President was "whining."

"Is anyone surprised Donald Trump has a problem with a strong woman? And we know that more is to come," Biden said. He called on "working people" to defend his new partner.

"Kamala Harris has had your back -- and now, we have to have her back," he said. "She's going to stand with me in this campaign, and all of us are going to stand up for her."

During an interview with Eric Bolling from "America This Week," a Sinclair program, Trump said Harris was not "liked" -- a gendered criticism that was often used to describe 2016 Democratic presidential nominee Hillary Clinton.

"She's not a person who's liked. I think people will fall out of love with her very quickly. Very quickly," Trump told Bolling. "She campaigned, and she campaigned very hard. Whenever people heard her open her mouth, she went down."

Biden also did not let the historic nature of his pick go unnoticed at their first event together. As Harris looked on, now firmly in the role of a supporting player, Biden imagined the reaction of "little Black and brown girls, who so often feel overlooked and undervalued in their communities."

"Today, just maybe," he said, "they're seeing themselves for the first time in a new way."