Democrats choose Biden to end 'chaos'

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

On Tuesday, viewers tuning in to Day 2 of the four-day Democratic National Convention saw presenters affirm Biden's character and leadership while drawing a sharp contrast with the brash Republican scrambling to remain in the White House after November's election.

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 that cemented the 77-year-old Biden's role as the party flagbearer.

The nomination was a formality as he had already won the majority of the more than 3,900 delegates back in June.

The roll call came on Day 2 of the mostly virtual Democratic convention aimed at celebrating the party's candidate and welcoming independents and frustrated Republicans into their political movement to oust 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 from 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."

His fellow heavy hitter also appearing virtually was Carter, who noted that the country deserves a leader with integrity and judgment, someone who is "honest and fair". "Joe has the experience, character, and decency to bring us together and restore America's greatness," he said.

Live speech next week

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.

He 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 Tuesday visit 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 formally accepts his party's nomination at the online Republican convention.

Former Democratic president Barack Obama was scheduled to speak on Wednesday night along with 2016 Democratic presidential nominee Hillary Clinton.

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

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

In another development, with political turmoil bubbling less than three months before the election, 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.

Louis DeJoy suspended all mail service changes, acceding to pressure by Democrats, who interpreted the moves as fashioned to boost Trump's reelection chances.

The reversal follows complaints that the cuts could slow the handling of mail-in ballots, which could account for as many as half of all votes cast in the election as the coronavirus pandemic raises fears of crowds at polling places.

The abrupt reversal from DeJoy, who is set to testify on Friday before the Senate, came after more than 20 states, from New York to California, announced they would sue to stop the changes.

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