Former US Vice President Joe Biden announced his candidacy to stand for the presidency in 2020, in a video posted to Twitter on Thursday.

"If we give Donald Trump eight years in the White House, he will forever and fundamentally alter the character of this nation," Biden said. "Who we are. And I cannot stand by and watch that happen."

Polling shows that Biden, who served as Barack Obama’s vice president for eight years, has a strong chance of eventually being nominated as the Democratic candidate.

A survey by polling data aggregator RealClearPolitics reveals him to be the favorite among Democratic voters, on 29.3%, followed by independent Senator Bernie Sanders on 23%t.

When making his declaration, Biden said the core values of the US and the nation's standing in the world were at stake.

In the video, Biden focused on the deadly 2017 clashes between white supremacists and counterprotesters in Charlottesville, Virginia. He was particularly critical of Trump's assertion that there were "very fine people" on both sides.

 "With those words, the president of the United States assigned a moral equivalence between those spreading hate and those with the courage to stand against it," Biden said.

Read more: 'History has not delivered its verdict': Ben Rhodes on Obama's legacy

In response to the news, Obama said that selecting Biden had been "one of the best decisions" he had ever made. The former US president is not expected to give any formal endorsement until much later in the nomination process. 

The announcement marks an unofficial end of the chaotic early phase of the 2020 presidential season. At least 20 Democrats are now in the running for the chance to take on Trump next year, with a possibility that some lesser-known candidates might still join the field.

amp/rc (AP, dpa, AFP)

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