Hillary Clinton has urged voters to support Joe Biden to prevent Donald Trump from being able to "sneak or steal his way to victory".
Addressing the Democratic National Convention on Wednesday from her home in Chappaquiddick, New York, Mrs Clinton said she hoped Mr Trump would put his ego aside and be the president America needs, but that hasn't happened.
"I wish Donald Trump knew how to be a president because America needs a president right now," she said.
"For four years, people have said to me, 'I didn’t realise how dangerous he was.' 'I wish I could go back and do it over.' Or worst, 'I should have voted.'
"Well, this can’t be another woulda' coulda' shoulda' election."
But "he is who he is," Mrs Clinton added. "America needs a president who shows the same compassion, determination, and leadership in the White House that we see in our communities."
The former presidential candidate reminded people of her 2016 loss despite winning 3 million more votes than Mr Trump.
Recalling a moment when Mr Trump asked Black voters in 2016 what they had to lose by supporting him, Clinton said: "Now we know."
As the first woman nominated for president in America, Mrs Clinton is also recalling the 100-year anniversary of the ratification of the 19th Amendment.
Mrs Clinton said she knows about "the slings and arrows" that vice presidential candidate Kamala Harris will face as a Black woman on the ticket."Believe me: This former district attorney and attorney general can handle them all," she added.
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Democrats also broadcast videos highlighting Mr Trump's crackdown on immigration, opposition to gun restrictions and his decision to pull out of the Paris climate accord.
Nancy Pelosi, the first woman Speaker of the US House of Representatives, told the convention she had seen firsthand Trump's "disrespect for facts, for working families, and for women in particular a disrespect written into his policies toward our health and our rights.
"But we know what he doesn't that when women succeed, America succeeds."
The first two nights of the four-day Democratic convention showcased statesmen and rising stars in the party who said Mr Biden's election would repair a pandemic-battered United States and put an end to the chaos of Mr Trump's four years in office.
The Republican National Convention, also largely virtual, takes place next week.
Additional reporting by Associated Press.