Bernie Sanders dubbed Donald Trump a racist, sexist and “pathological liar” on Tuesday as he launched a presidential bid by vowing to finish the “revolution" he started in 2016.

The US senator from Vermont called for a million people to sign up to a grassroots campaign that aims to sweep him into the White House and “transform” political and economic life in America.

Mr Sanders, who calls himself a democratic socialist, outlined an unashamedly left-wing policy platform that included government-funded healthcare for all, free college tuition and a $15 minimum wage.

The 77-year-old will be hoping to reignite the enthusiasm that helped him outperform expectations against Hillary Clinton in the last race for the Democratic presidential nomination. He got 13 million votes to Ms Clinton’s 17 million.

However in the 2020 race competition is even fiercer, with more than a dozen established candidates expected to run and many adopting progressive policies that Mr Sanders has championed.