Bernie Sanders, the two-term Senator from Vermont rivaling Hillary Clinton’s bid for Democratic presidential nominee, has supporters showing up in full force at his campaign stops. In swing-state Colorado, 5,000 have already RSVPed to attend an event on Saturday, which will be the largest campaign trail crowd for any candidate so far in 2015.

The self-described socialist independent politician is seeking the democratic nomination against Hillary Clinton, who he warns will lead the United States to an oligarchy. He has also openly called for political revolution.

“I really was surprised,” Sanders said of the anticipated audience. “We’ve had very, very large and enthusiastic crowds,” he told AFP.

“I think we’re touching a nerve.”

Over 4,000 people came out to his event in Minnesota where Sanders spoke to his over-capacity audience of supporters on income inequality and oligarchy.

“You guys already own much of the economy. Now we’re going to give you the United States government and state governments all over this country. Brothers and sisters, that is not democracy. That is a movement toward oligarchy,” Sanders stated to huge applause.

In Wisconsin, Sanders is polling only eight points behind Clinton, despite her being depicted in the media as marching towards the nomination without competition.

As corporate special interests, workers’ rights, climate change, and other social issues are drawing concern from much of the country, Sanders is touted by many as the only candidate willing to discuss the issues directly impacting the nation in a straightforward, blunt, and meaningful way.

“Those core issues that he’s been talking about are the reason he is resonating so powerfully with people,” Tad Devine, a Sanders advisor and strategist, said on Thursday of the massive support the senator is receiving.

Unlike the other candidates, Sanders prides himself on having no super PAC to raise mass amounts of money. Still, he is not hurting for donations, and his many small donor contributions are adding up. Devine says the campaign is on track to raise $40-50 million before next year’s primary.

Despite his huge grassroots support, however, experts are still calling him an outsider, competing against Clinton who is as inside as it gets.

Many argue that those experts are underestimating the levels of frustration among Americans with the gap between wealthy, powerful policy leaders and the people.

On Friday, the Ready for Warren campaign, which is calling for Elizabeth Warren to run against Clinton, launched a new initiative called Ready to Fight, which will also be endorsing Bernie Sanders.