Transcript for Bernie Sanders an Unlikely Source of Competition for Hillary Clinton
would be such a jerk. Something having is brewing in the race for the white house. Hillary Clinton may have vigorous competition from an unlikely source, this guy, ab scour senator from Vermont who has for years self-identified as a socialist. Bernie sanders is now drawing huge crowds raising big money and climbing in the polls. Here's ABC's linsey Davis. Oh. Reporter: Support for Bernie sanders for president is surging. The turnout of roughly 10,000 at a campaign rally earlier this week in Wisconsin seemed to surprise even sanders. In case you haven't noticed a lot of people are here. Reporter: While the 73-year-old Brooklyn born self-described democratic socialist from Vermont has raised $15 million so far, just one-third of the money Hillary Clinton has raised sanders may just give her a run for her money. Tonight, we have more people at a meeting for a candidate for president of the United States than any other candidate has had in 2016. Reporter: Polls show he's quickly closing the gap in new Hampshire and Iowa. The Vermont senator is calling for a grassroots political revolution to get big money out of politics. So far, he says 99% of his contributions have come from individuals giving $250 or less. Bernie sanders is shaping up to be the anti-hillary right now. There is a big element of the democratic party that wants an alternative. Reporter: Many of his supporters tout him as the honest and authentic candidate. Hillary needs to consult with her focus group and get back to you in a couple of weeks. It's about time that someone actually stood that we know is on our side. Reporter: Just for perspective when president Obama was running for his first term as president almost three months into his candidacy he had 100,000 donors. Sanders just two months in has 250,000, so just a few weeks ago he seemed like a long shot. He still may be but there is a sanders movement right now. Interesting story.
This transcript has been automatically generated and may not be 100% accurate.