Democratic presidential candidate Joe Biden has named Senator Kamala Harris as his running mate - the first black woman and Asian American in the role.
Once a rival for the top job, the California senator of Indian-Jamaican heritage had long been considered the front-runner for the number two slot.
The former California attorney general has been urging police reform amid nationwide anti-racism protests.
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Mr Biden will face President Donald Trump in the election on 3 November.
At a White House news conference on Tuesday, Mr Trump, a Republican, described Ms Harris as "my number one draft pick".
Ms Harris will debate Mr Trump's running mate, Vice-President Mike Pence, on 7 October in Salt Lake City, Utah.
Only two other women have been nominated as vice-presidential candidates - Sarah Palin by the Republican party in 2008 and Geraldine Ferraro by the Democrats in 1984. Neither ended up on the winning ticket.
A woman of colour has never been appointed to a presidential ticket by either of the two main American political parties. No woman has won the US presidency either.
What did Biden and Harris say?
Mr Biden tweeted that he had "the great honour" to name Ms Harris as his number two.
He described her as "a fearless fighter for the little guy, and one of the country's finest public servants".
He noted how she had worked closely with his late son, Beau, when she was California's attorney general.
"I watched as they took on the big banks, lifted up working people, and protected women and kids from abuse," he tweeted.
"I was proud then, and I'm proud now to have her as my partner in this campaign."
