Hillary Clinton is all but certain to run for the White House again in 2020, according to a former aide.

Mark Penn said the Democrat had “an unfinished mission to be the first female president” and “a personal grievance” against Donald Trump, who vowed to imprison her before emerging victorious in the 2016 vote.

“She will not allow this humiliating loss at the hands of an amateur to end the story of her career,” he wrote in a Wall Street Journal article co-authored by former Democrat politician Andrew Stein.

Mr Penn was a senior aide to Ms Clinton and her husband Bill from 1995 to 2008 and was chief strategist for her failed campaign for the Democratic nomination a decade ago.

Ms Clinton has previously insisted she would not seek to run again, although last month she appeared to hint at a change of stance, admitting: “I’d like to be president.”

Mr Penn and Mr Stein said the former secretary of state “has had two years to go over what she did wrong” in 2016 and would “come out swinging” with a strategy for defeating Mr Trump.

“You can expect her to run for president once again,” they wrote. “Maybe not at first, when the legions of Senate Democrats make their announcements, but definitely by the time the primaries are in full swing.”

Ms Clinton would reinvent herself as a liberal firebrand to “easily” capture the Democratic nomination, Mr Penn and Mr Stein predicted.

“She will hope to emerge as an unstoppable force to undo Mr Trump, running on the #MeToo movement, universal health care and gun control,” they wrote.

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Long-time confidants of Ms Clinton poured hot water on the prediction she would run again in two years.

“She’s more likely to win Powerball,” Philippe Reines, her former adviser, told The Hill.

But Mr Penn and Mr Stein said: “Don’t pay much attention to the ‘I won’t run’ declarations. Mrs Clinton knows both Mr Clinton and Mr Obama declared they weren’t running, until they ran.”

Kellyanne Conway, one of Donald Trump’s most senior advisers, mocked the idea of Ms Clinton’s comeback.