(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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