Bernie Sanders has responded to Hillary Clinton’s criticism of his rival election campaign by suggesting she lost to “the most unpopular candidate in history”.

Mr Sanders said progressives needed to “go forward” together to fight the conservative policies of President Donald Trump.

His campaign for the Democratic nomination was widely popular and was a serious thorn in the side of Ms Clinton as she tried to gain support for the position, which she eventually won.

In excerpts of her memoir, What Happened, due to be released this month, Ms Clinton accused Mr Sanders’ campaign attacks of causing “lasting damage”.

Bernie Sanders: DACA decision is 'ugliest and most cruel ever made by a president in modern history'

She said these made it “harder to unify progressives in the general election”.

These attacks, by way of "innuendo and impugning my character," also enabled Mr Trump to turn the phrase ‘Crooked Hilary’ into a campaign slogan, she added.

But speaking on Stephen Colbert’s ‘The Late Show’, Mr Sanders responded by claiming progressive politics was stronger than it had been for many years.

“We have got to stand together against Trump’s efforts to divide us up,” he said.

But Mr Sanders also added a jibe: “Secretary Clinton ran against the most unpopular candidate in this history of this country and she still lost.

“But our job now is not to go backwards, it is to go forwards.”

He spoke of the need to fight Mr Trump’s plans to cut Deferred Action for Childhood Arrivals (DACA), an Obama-era policy which protects nearly 800,000 people who were brought into the US as children by illegal immigrants.

Mr Sanders also stressed the need for the President’s opponents to work together.

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He said: “I think the response is we have got to think going forward and I would like her to join us in a fight for 15 [dollar minimum wage], in a Medicare-for-all single payer system, in taking on the fossil fuel industry so that we transform our energy system away from fossil fuel and move to energy efficiency and sustainable energy.”