These Photos Of Bernie Sanders' Crowds Of Supporters Might Just Give Hillary Clinton Reason To Worry

While the Republican field of presidential candidates continues to grow, only a handful of Democrats have officially launched campaigns so far, with former Secretary of State Hillary Clinton the presumed front-runner. But according to The Washington Post, more than 5,500 people showed up to hear Sen. Bernie Sanders in Denver on Saturday, in what the Post called one of the largest candidate rallies of the 2016 campaign so far. Sanders spoke in the Hamilton Gymnasium at the University of Denver, but the gym was so crowded that the audience spilled over into an nearby atrium and an adjacent lacrosse field outside, the Sanders campaign and university officials told the Post.

This isn't the first time the left-leaning, 73-year-old, wild-haired senator from Vermont has drawn larger-than-expected crowds; in fact, that's starting to become his thing. The New York Times reported in May that as Sanders toured Iowa, the state which has the crucial first caucus next February, he routinely spoke to packed community centers at town-hall style meetings, even though at the time he had a fraction of the infrastructure and staff that Clinton did in the Hawkeye State.

And there have been other rallies with similar surprise turnouts. At his kickoff in Burlington, Vermont, about 5,000 people showed up, and nearly 3,000 Sanders supporters came to a rally a few days later in Minneapolis, according to MSNBC. And at a rally in New Hampshire earlier this month, it was standing room only in the college town of Keene, as close to 1,000 people came to hear Sanders' speech on income inequality.

During that speech, Sanders seemed optimistic, telling the audience, "Let me tell you a secret. We're going to win New Hampshire," according to The Keene Sentinel.

While most polls give Clinton a healthy edge over Sanders, he's a formidable candidate many are warning Clinton not to underestimate. The self-proclaimed socialist was an early champion of civil rights, and is not afraid to challenge the status quo, as when he wrote a letter to President Obama asking him to raise taxes on the rich. Sanders also has the distinction of being the longest-serving Independent in Congress, with 16 years in the House and eight years so far in the Senate.

And it might be worth it for Clinton to heed warnings about Sanders. After all, she's been in this position before. Despite being an early front-runner in 2008, Clinton's campaign was overtaken by a charismatic upstart from Illinois who many underestimated early on: then-Senator Barack Obama. While Sanders might not have the groundswell of support Obama built, he's tapped into something, a feeling or a sentiment, that inspires people to show up and hear what he has to say.

Images: (1); Instagram/BernieSanders