Senator Bernie Sanders, whose insurgent 2016 presidential campaign reshaped Democratic politics, has announced that he is - taking aim at Donald Trump as a "racist" and a "pathological liar."
A self-described democratic socialist, Sanders made an unsuccessful run for the presidency in 2016 whose progressive themes inspired a younger generation of voters.
"We are living in a pivotal and dangerous moment in American history. We are running against a president who is a pathological liar, a fraud, a racist, a sexist, a xenophobe and someone who is undermining American democracy as he leads us in an authoritarian direction," Sanders said in a video.
Sanders, an independent who caucuses with Democrats, highlighted policies he will advocate on the campaign trail: healthcare for all, raising the minimum wage to a "living wage," and combatting climate change.
"Our campaign is about transforming our country and creating a government based on the principles of economic, social, racial and environmental justice," Sanders said.
He vowed to take on "powerful special interests that dominate our economic and political life," listing Wall Street, health insurance companies and the military-industrial complex.
Trump's campaign quickly hit back, saying that while Democrats may have embraced ideas Sanders advocates, the American people have not.
"Bernie Sanders has already won the debate in the Democrat primary, because every candidate is embracing his brand of socialism," the Trump campaign said in a statement.
"But the American people will reject an agenda of sky-high tax rates, government-run health care and coddling dictators like those in Venezuela."

Bernie Sanders holds hands with fellow presidential challenger Tulsi Gabbard. Source: AAP
Sanders gave an outline Tuesday of how he will campaign.
"What I promise to do is, as I go around the country, is to take the values that all of us in Vermont are proud of -- a belief in justice, in community, in grassroots politics, in town meetings -- that's what I'm going to carry all over this country," he said in an interview with Vermont Public Radio.
In his video, Sanders said he aims to run "an unprecedented grass-roots campaign of one million active volunteers in every state in our country."
Sanders benefitted from just such a groundswell in 2016 but lost the Democratic nomination to establishment favorite Hillary Clinton. She in turn was defeated by Trump, a billionaire who campaigned as a populist outsider.
Sanders garnered passionate support among young liberals with his calls for universal health care, a $15 minimum wage and free public university education.
In his announcement video, Sanders said the policies he advocated in 2016 campaign have made their way into the political mainstream and it is now time to "complete that revolution."
"We were told that our ideas were 'radical' and they were 'extreme,'" he said.
"We were told that Medicare for all, a $15-an-hour minimum wage, free tuition at public colleges and universities, aggressively combatting climate change, demanding that the wealthy start paying their fair share of taxes -- we were told that all of these concepts were ideas that the American people would never accept," Sanders said.
"All of these policies and more are now supported by a majority of Americans. Together, you and I and our 2016 campaign, began the political revolution. Now it is time to complete that revolution and implement the vision that we fought for."