Sen. Bernie Sanders of Vermont made his populist presidential pitch to an energized crowd of more than 7,500 people in Portland on Monday night, pledging to fight for universal health care, free college tuition and a “living wage,” and against what he sees as the corruptive influence of big money on American politics.

An independent running for the Democratic nomination in 2016, Sanders is a progressive stalwart whose campaign appears to be gaining steam in early voting states against a better known and better financed Democratic front-runner, Hillary Clinton.

Sanders arrived in Portland – likely selected because of its leftist lean and proximity to New Hampshire – after sizable rallies in other states. And although exact figures weren’t available Monday night, staff at Portland’s Cross Insurance Arena estimated that the crowd could have exceeded 8,000 in the roughly 9,000-capacity arena for an event originally planned as more of a town hall-style forum than a rally. Organizers delayed the start of the 7 p.m. event because so many people were still lined up down the block outside the arena.

“From Maine to California – and we have friends in Alaska and Hawaii as well – the American people understand that establishment politics and establishment economics is not working for the middle class,” Sanders said. “They understand that the greed of Wall Street and the greed of corporate America is destroying the great middle class of this country. And people are saying from coast to coast, ‘You can’t keep getting away with that.’ ”

Despite the size and enthusiasm of the Maine crowd, Sanders faces an uphill battle against Clinton and potentially other contenders in the 2016 Democratic primaries and caucuses nationwide. And Sanders’ staunchly anti-corporate message and unabashedly liberal policy stances – and his past description of himself as a socialist – would likely pose a challenge in the general election.

The crowd clearly skewed young, but included Mainers of all ages, drawn by a politician whose populist message appears to resonate with voters disenfranchised by the “mainstream” Democratic Party. Sanders hit many of the bedrock principles of progressive Democrats as he vowed to hold Wall Street more accountable, to fight for guaranteed paid maternity leave and vacation time, to push for universal health care and to invest more money in schools, but less in prisons.

He vowed to only nominate Supreme Court justices who will vote to overturn the Citizens United campaign finance decision, while praising the recent court decision effectively legalizing same-sex marriage nationwide. The former Burlington mayor and veteran member of Congress blasted free-trade agreements also unpopular with many in Maine and expressed support for a $15-an-hour minimum wage, calling the current federal minimum of $7.25 an hour “a starvation wage.”

The crowd – some holding “Feel the Bern” signs – cheered loudly when Sanders repeatedly pledged to take on corporate interests, including by imposing higher taxes on “Wall Street speculators” and on the wealthy. He called the gap between the wealthy and the poor in the U.S. “a disgrace.”

“The taxpayers of this country bailed out the illegal behavior of Wall Street. It is time for Wall Street to bail out the middle class,” Sanders said.

Sanders, who is 73, has represented Vermont in Congress since 1991, including the past eight years in the U.S. Senate. He is one of two independents in the Senate, along with Maine’s Angus King, both of whom caucus with the Democrats.

Sanders rallied his supporters in Maine as his campaign is gaining traction among voters in New Hampshire and Iowa, the first two primary and caucus states in the 2016 race. Although often described as a long-shot, Sanders trailed Clinton by just 8 points among New Hampshire Democrats in a CNN poll released last week. A Quinnipiac University poll showed Sanders trailing the former Secretary of State and first lady by 19 percentage points among Iowa Democrats, but the gap had been 45 points in May.

Clinton campaign spokeswoman Jennifer Palmieri told MSNBC’s Morning Joe program on Monday that the campaign is not surprised to see Sanders faring well, but that it won’t affect Clinton’s focus on meeting voters in the two states at as many small events as possible as opposed to large rallies.

“We’re worried about him, sure,” Palmieri said. “He’s a force and he’ll be a serious force for the campaign, and I don’t think that will diminish. We’ve said from the start … that it’s going to be really competitive.”

Sanders is the second presidential hopeful in less than a week to visit Portland, which shares a media market with parts of New Hampshire. New Jersey Gov. Chris Christie stopped by Becky’s Diner last Wednesday – one day after he formally announced his presidential bid – in order to pick up an endorsement from his friend and fellow Republican Gov. Paul LePage.

Sanders was introduced Monday by former state Sen. Troy Jackson, an Allagash Democrat who serves as one of the three members of the Democratic National Committee from Maine. Also a fiery speaker with a strong populist bent, Jackson said Sanders represents “everything we hope for in a progressive future.” Jackson added that he was “ready for a president who does not fear taking on the millionaires and billionaires of Wall Street the way Bernie Sanders so fearlessly does.”

Many in Monday’s crowd were younger, such as a recent high school graduate from the Boston area who drove to Maine with a parent to hear Sanders.

“He really does say what he believes, and just seeing how people respond to that, I wanted to be part of it,” said Benjamin Powell, an 18-year-old from Dedham, Massachusetts.

Yarmouth residents Jonas Allen and Beth Brewer came with their two young boys, 6-year-old Ellis and 10-year-old Levi, to hear a candidate that Allen said is putting the middle class ahead of corporate or financial interests.

“I think that’s why he is taking off because he is the only candidate on the Republican or the Democratic side who is really taking a stand on the issue,” Allen said. “When you have the political machine behind you like the Clintons do, it is going to be a challenge. But I think his populist message is getting out there whether he gets the nomination or not.”

There were plenty of older supporters in the crowd, as well.

Among those who had arrived early enough to get front-row seats in the arena were Dale and Robyn Moreau and Rose and Jack Kennealy, all of Cape Elizabeth.

“This is the first candidate to be excited about since Eugene McCarthy,” said Dale Moreau, referring to the 1968 presidential hopeful.

“He is genuine,” said Robyn Moreau.

“And he is not naive about working in Washington,” added Rose Kennealy.

Walking away from the arena afterward, Falmouth resident Jackie Curley said every single issue that Sanders highlighted on Monday is important to her.

“For the last 20 years, we have needed somebody like him,” Curley said. “We have had many good people, but nobody like this guy.”