Kamala Harris has accepted her historic nomination as the US Democratic party's vice-presidential candidate, running with Joe Biden for the White House.
In a speech to her party convention, the first US woman of colour on a major-party ticket assailed President Donald Trump's "failure of leadership".
The California senator pledged to speak "truths" to the American public.
Mr Biden and Ms Harris will challenge Mr Trump and his Vice-President Mike Pence in the election on 3 November.
The coronavirus pandemic has forced Democrats to abandon the cheering throngs, fanfare and razzmatazz of the typical party convention in favour of a virtual event of pre-recorded and live speeches.
The grand finale of the four-night conference will see Mr Biden, the Democratic presidential nominee, deliver a speech on Thursday.
What did Kamala Harris say?
"We're at an inflection point," she said, speaking live from a largely empty hotel ballroom in Mr Biden's hometown of Wilmington, Delaware.
Attacking Mr Trump, she continued: "The constant chaos leaves us adrift. The incompetence makes us feel afraid. The callousness makes us feel alone. It's a lot.
"And here's the thing: We can do better and deserve so much more.
"We must elect a president who will bring something different, something better, and do the important work."
Ms Harris - the child of immigrants from India and Jamaica - pledged that she and Mr Biden would revive a country fractured by the coronavirus pandemic and racial tension.
"There is no vaccine for racism," she said. "We've got to do the work."
She continued: "Donald Trump's failure has cost lives and livelihoods."
"Right now, we have a president who turns our tragedies into political weapons," she added.
President Trump swiftly hit back, tweeting about Ms Harris' previous attack on Mr Biden over his record on race issues, while they were both rivals for the Democratic White House nomination.
BUT DIDN’T SHE CALL HIM A RACIST??? DIDN’T SHE SAY HE WAS INCOMPETENT???— Donald J. Trump (@realDonaldTrump) August 20, 2020
The moment came during a live TV debate last year, though Ms Harris prefaced those remarks by telling Mr Biden: "I do not believe you are a racist."
Also on Wednesday, former US President Barack Obama launched his most withering direct attack yet on Mr Trump, accusing his Republican successor of treating the White House like "one more reality show".
A post-apocalyptic speech
The now-official Democratic vice-presidential nominee faced a bit of a challenge, having to directly follow Barack Obama, the party's most beloved and rhetorically gifted politician.
What Ms Harris offered was a bit of an amalgam - one that sometimes connected and occasionally plodded. It was part biographical introduction, part sales pitch for Mr Biden and - most notably - part frontal attack on structural racism.
Although she's been attacked by some on the left for her prosecutorial background, Ms Harris tried to turn that into a benefit for a general election audience, speaking of how she always tries to fight for justice.
Her speech delivered with smiles and warmth, but it took place in a rather haunting environment - a room constructed to replicate a party convention hall, but devoid of the cheering crowds.
It all had a slightly post-apocalyptic feeling, which makes it seem that the emptiness of the current pandemic-stricken nation is a feeling Democrats want to highlight - and lay at Mr Trump's feet.
The first black woman and South Asian American on a major US presidential ticket, she said she inherited a passion for public service from her immigrant mother, Shyamala Gopalan, a biologist.
"I keep thinking about that 25-year-old Indian woman, all of five feet tall, who gave birth to me.
"On that day, she probably could have never imagined that I would be standing before you now and speaking these words: I accept your nomination for vice-president of the United States of America."
Ms Harris is a former San Francisco district attorney and California attorney general who joined the Senate in 2017.
She made headlines by grilling two Trump nominees, Brett Kavanaugh for Supreme Court justice and William Barr for attorney general, during Senate committee hearings.
Ms Harris launched her presidential bid in January last year as a top-tier candidate, only to see her campaign fizzle amid criticism that she had struggled to articulate a coherent vision for office.
Who else spoke at the convention?
Mr Trump's predecessor Barack Obama launched a fierce attack on the current occupant of the White House.
Mr Obama, who has largely avoided attacks on Mr Trump since leaving office, accused him of treating the US presidency like "one more reality show".
The former US president said his Republican successor "hasn't grown into the job because he can't".
At the White House, Mr Trump hit back that he was only elected because of the "horror" Mr Obama left Americans.
On Wednesday night, Hillary Clinton, the 2016 Democratic nominee, also assailed the man who thwarted her White House ambitions.
Speaking from her home in Chappaqua, New York, she said: "I wish Donald Trump had been a better president. But, sadly, he is who he is."
Gabrielle Giffords, the former Arizona congresswoman who was shot in the head when greeting supporters in 2011, highlighted gun violence in the US.
"Words once came easily, but today I struggle to speak. But I have not lost my voice," she said.
"America needs all of us to speak out, even when you have to fight to find the words. We are at a crossroads. We can let the shooting continue, or we can act. We can protect our families, our future. We can vote."