Watch CNN’s Gloria Borger interview Sen. Bernie Sanders on CNN’s “New Day” on Monday.

CNN —  

Bernie Sanders used fiery language at a rally Sunday to fight against the attitude that “politics is bulls—,” and urged his supporters to push back against big money in elections.

Slamming the Koch brothers and decrying America’s slide into “oligarchy,” the Democratic presidential candidate energized an eager crowd in Las Vegas with his colorful language and a trademark salvo against the influence of mega donors.

Sanders challenged the audience, “People are going to say, ‘Why did you go to this rally? Some guy no one has ever heard of? Why were you here?’ And I want you to tell them, if anyone tells you politics is bulls—, and you shouldn’t get involved, ask them why it is that the Koch brothers and other billionaires are spending 900 million bucks on this election?”

He continued, “They think it’s pretty important, and if they think it’s pretty important, then your friends should think it’s pretty important.”

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The Vermont senator put the Koch brothers in sharp focus throughout his speech, spotlighting the conservative billionaire donors and their 2016 fundraising pledges as a symbol of a corrupt political process.

“The situation is so absurd and so harmful to our democracy that right now,” Sanders railed, “you have one family, the second wealthiest family in America … and a few of their friends are going to spend $900 million on this campaign.”

“That is more money than will be spent by either the Democratic Party or the Republican Party,” he noted, adding, “When you have one family spending more money than either of the two major political parties, my friends, that is not called democracy, that is called oligarchy, and we are not going to allow that to continue.”

Sanders has been polling behind Democratic primary front-runner Hillary Clinton, but he’s been able to draw sizable crowds for rallies like the one on Sunday night in part because of his sharp messaging and targeting liberal principles surrounding economic inequality.