Sen. Bernie Sanders , the Vermont Independent whose 2016 campaign for the presidency helped shift the Democratic Party to the left on issues like “Medicare for All” and free college tuition, announced on Tuesday that he is running for president again. The self-described democratic socialist immediately set an ambitious target for his supporters, calling on them “to be part of an unprecedented grassroots campaign of 1 million active volunteers, in every state in our country.”

I'm running for president. I am asking you to join me today as part of an unprecedented and historic grassroots campaign that will begin with at least 1 million people from across the country. Say you're in: https://t.co/KOTx0WZqRf pic.twitter.com/T1TLH0rm26 — Bernie Sanders (@BernieSanders) February 19, 2019

Sanders made the appeal across his popular social media accounts, in a variety of forms.

Have you joined the team yet? Add your name to say you're in: https://t.co/RPn2ahN7rq pic.twitter.com/nqc7sqKBRc — Bernie Sanders (@BernieSanders) February 19, 2019

The appeal was also featured in an 11-minute YouTube video, in which Sanders laid out the rationale for his campaign, offering far more specifics on policy than rivals like Sen. Kamala Harris, whose website lacks a policy section.

Hours before Sanders joined the race, Harris was asked by Fox News if his popularity in New Hampshire meant that she needed to move further to the left to compete in that state’s primary. “I will tell you that I am not a democratic socialist,” she replied.

Another rival who is far closer to Sanders on the issues, and who has laid out specific, radical policies, Sen. Elizabeth Warren, has attempted to distinguish herself from him by telling reporters, like Ruby Cramer of Buzzfeed News, that the core difference between the two is that “he’s a socialist, and I believe in markets.” “I am a capitalist,” Warren told John Harwood of CNBC last year. “I believe in markets. What I don’t believe in is theft; what I don’t believe in is cheating,” she added. In an interview with CBS News, Sanders dismissed concerns that President Donald Trump would try to associate him with the collapse of Venezuela’s socialist experiment and defended his brand of democratic socialism in common-sense terms. “When I talk about democratic socialism, if somebody wants to call me a radical, okay, here it is: I believe that people are inherently entitled to health care,” Sanders said. “I believe people are entitled to get the best education they can. I believe that people are entitled to live in a clean environment.”