Vermont lawmaker-turned-Democratic presidential hopeful Bernie Sanders may be proving this week that he won't be outrivaled or outnumbered in support, having hosted a huge, record-breaking crowd who cheered him on raucously at a Wisconsin rally.

The gathering in Madison for the 73-year-old Vermont junior Senator — a self-declared democratic socialist known for his progressive stances on income equality — drew some 10,000 supporters, who packed into the Veterans Memorial Coliseum Wednesday night in the home state of conservative Governor Scott Walker, a presumptive candidate for the Republican nomination who is expected to announce his bid in the next few weeks.

"Tonight we have made a little bit of history. Tonight we have more people at any meeting for a candidate of president of the United States than any other candidate," Sanders said, referring to rallies that have occurred this year.

The crowd in Madison, a largely liberal bastion in the mostly conservative state, whistled and applauded throughout Sanders' speech — except at any mentions of Walker, which prompted a sea of boos and hisses.

State Republicans in Wisconsin welcomed Sanders this week by erecting giant billboards across the state, which featured Sanders and Clinton with their heads superimposed onto the bodies of characters from the film Dumb and Dumber. The image is featured in front of a picture of the White House and branded with the slogan "Left and Lefter," placing Sanders on the more extreme end for his liberal policies.

On Wednesday, Sanders took to the opportunity to dig into Walker, calling out the conservative governor and supporters for their own class of "extremism."

"The billboard indicated that I was an extremist," Sanders said. "So let me just say a few words to my friends in the Republican Party about extremism: When you deny the right of workers to come together in collective bargaining, that's extremism. When you tell a woman that she cannot control her own body, that's extremism. When you think a woman is a child and can't purchase a contraceptive, that is extremism. When you give tax breaks to billionaires, and refuse to raise the minimum wage, that's extremism."

Photo via Republican Party of Wisconsin website.

The turnout and enthusiasm Sanders has seen since launching his campaign — including his creeping support in early primary and caucus states like Iowa — suggests he may have more of an edge on presidential hopeful Hillary Clinton, who is currently the Democratic clear frontrunner, than previously thought.

Sanders has also previously criticized Clinton's ties to Wall Street, and the former secretary of state's inability to confront the widening income gap in America.

"Is Hillary Clinton, are other candidates, prepared to take on the billionaire class?" Sanders told reporters in Washington in April. "Based on her record, I don't think so," he said.

Clinton's camp has hit back, calling Sanders "unrealistic," and has chastised him for sending an "extreme message."

This is also a theme also seized upon by Walker and other conservatives. Prior to Wednesday's event, a public spat came to a boil between Walker, who has famously sought to shut down collective bargaining and union rights for workers throughout his tenure as governor, and Sanders, who has championed hiking minimum wages to $15 and raising taxes on the wealthy.

"Bernie Sanders is right about one thing: we don't need another Clinton in the White House," he said in a statement. "On virtually every other issue, however, he stands in stark opposition to most Americans. Wisconsinites have rejected his top-down, government-knows-best approach three times in the last four years."

Walker's statement referred to the fact that since 2010 he has won Wisconsin three elections.