Biden touted as leader to end 'chaos'

US Democrats nominated Joe Biden on Tuesday as their 2020 presidential candidate, calling the Washington veteran a "man of courage" who would sweep away what they characterized as the "chaos" of four years under Republican President Donald Trump.

Viewers tuning in to the second day of the four-day Democratic National Convention saw presenters affirm Biden's character and leadership while drawing a sharp contrast with Trump.

In an unprecedented and elaborate roll-call vote that took place entirely online due to the coronavirus pandemic, all 50 states and seven territories announced their vote tallies, cementing the 77-year-old Biden's role as the party flag-bearer.

"Well thank you very, very much, from the bottom of my heart," a beaming Biden said in a live video link.

The nomination was a formality, since he already had won the majority of the more than 3,900 delegates.

The second day also saw the party celebrate its candidate and open its arms to independents and frustrated Republicans in an effort to remove Trump from the White House.

The proceedings included a series of presentations by party leaders past and future who unleashed their own arguments against the White House incumbent and urged voters to rally around Biden.

The lineup featured 95-year-old Jimmy Carter, who served one presidential term starting in 1977, and 1990s commander-in-chief Bill Clinton, who warned that the Trump White House is swirling with chaos instead of the competence necessary to address the nation's crises.

"At a time like this, the Oval Office should be a command center. Instead, it's a storm center. There's only chaos," said Clinton, who turned 74 on Wednesday. He had prerecorded his address from his home in New York.

"Just one thing never changes－his determination to deny responsibility and shift the blame. The buck never stops there," Clinton added.

Carter, who said the country deserves a leader with integrity and judgment, someone who is "honest and fair", also appeared virtually.

"Joe has the experience, character and decency to bring us together and restore America's greatness," Carter said.

Trump, 74, faced a barrage of criticism on opening night, too, notably from former first lady Michelle Obama, who said the president lacks the character and skills for the job.

The president tweeted on Tuesday: "People forget how divided our country was under (Barack) Obama and Biden. The anger and hatred were unbelievable. They shouldn't be lecturing to us. I'm here, as your president, because of them!"

On a visit on Tuesday to battleground state Arizona, Trump knocked Michelle Obama for delivering taped remarks.

"Thursday night, I'm doing it live," Trump said, referring to his speech next week when he will formally accept his party's nomination at the online Republican National Convention.

Former Democratic president Obama was scheduled to speak on Wednesday night, along with 2016 Democratic presidential nominee Hillary Clinton and Biden's running mate, Kamala Harris.

William A. Galston and Elaine Kamarck, both senior fellows of governance studies at the Brookings Institution, said in a research note that the Democrats need to use the gathering to lay out a vision for the future that appeals to a broad swath of voters, and make the case against Trump and his congressional supporters without turning off suburban Republicans and independents.

Just one incumbent president has been defeated in the past four decades.

Hillary Clinton had said that if Biden and Harris win, the work before them will be "rather overwhelming".

In a video talk with the Atlantic Council broadcast on Monday, she called US ties with China the "most consequential of our global relationships" and predicted that a Biden-Harris administration would aim to set the US "relationship with China back on a steadier, more predictable course".

In another development, the US Postal Service chief moved to take a contentious issue off the table on Tuesday, saying no changes would be made to the system before the Nov 3 vote, which will include mailin ballots.

Zhao Huanxin in Washington,Ai Heping and Heng Weili in New York, and agencies contributed to this story.