Writing in the San Francisco Chronicle, Willie Brown said that Senator Harris should instead aim for the role of attorney general.

The former San Francisco mayor said that the role of vice president doesn't often open the doors to the job of president, but admitted that it would be an achievement if Harris were to become the first woman to ever hold the position.

Writing for the paper, Brown said: 'True, the vice president does have an advantage the next time the party needs a new nominee, which in Biden's case could be four years from now. 

'But in the meantime, the vice president has no real power and little chance to accomplish anything independent of the president.'

Brown also pointed out that the position of attorney general holds the power to decide every single US attorney in the country, offering real authority.