Sanders, a self-described democratic socialist, is drawing sizable crowds in the early voting states. He's also gaining against high-profile candidate Hillary Rodham Clinton in very early polls, particularly in New Hampshire, a factor that impresses the political class even though opinion surveys at this point are limited in predicting who will win.
"You're living in a country today which has more wealth and income inequality than any major industrialized nation on earth," Sanders said recently at a picnic south of Des Moines.
Clinton remains the race's overwhelming favourite, but there's no question the 73-year-old with the disheveled white hair isn't just a novelty.
"This is a unique individual," said Iowa Democratic state Rep. Scott Ourth, who introduced Sanders last weekend at the picnic in Indianola. "This guy has only one standard. If it's right for people, he's going to fight for it. If it's bad for people, he's going to take a stand against it."
Drawing unexpectedly large crowds, the campaign has moved a town meeting planned in Las Vegas on Friday into a more spacious venue. About 5,000 people are expected at a rally Saturday at the University of Denver.
Sanders is running with a relentless focus on policy. He rarely talks about his family, other than mentioning his four children and 7 grandchildren when explaining the importance of confronting climate change. In Minneapolis he was joined on stage by his wife, Jane, and noted they had just celebrated their 27th wedding anniversary.
He's promoting a massive government-led jobs program to fix roads and bridges. He wants a $15-an-hour minimum wage, and higher taxes on the wealthy and Wall Street. He advocates for a single-payer health care system, an expansion of Social Security benefits and debt-free college.
Sanders often points to some European and Scandinavian countries that provide subsidized or free education, universal health care and generous family leave policies as models for the U.S. He rarely mentions that tax rates in such countries are far higher than in the U.S. It's a style that couldn't be more different than Clinton's.
Hours before the first major rally of her campaign, Clinton released a Spotify playlist of songs, featuring music by Katy Perry, Kelly Clarkson and Sara Bareilles. One of her campaign Twitter feeds showed a green silhouette of her head wearing trendy headphones.
Clinton has been travelling with Secret Service agents since her husband's presidency in the 1990s.
Sanders shows up at rallies and events with a small contingent of aides. In Indianola, he carried a folded piece of paper scrawled with notes while he spoke.
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