"Trump and his friends should know that there are millions of people who will not stand for their greed at the expense of the working class," Senator Sanders said in an email message to his supporters, sent minutes before Trump was sworn-in as the 45th President of the United States.
The organisation created by Sanders after post-primary loss, "Our Revolution" sought donations from its supporters to fight out against the new administration.
"It can be the day that we declare that we are going to stand with our brothers and sisters who are staring at the threat of mass deportation. That we will not let anyone divide us up by race, nationality, gender, or sexual orientation," Jackson said.
"Together we have built the largest progressive grassroots movement this country has ever seen. And right now, we have an opportunity to send a powerful message to Donald Trump and Republicans in Congress: we are not going to let them drag us backward," the email said.