US Senator and Democratic presidential candidate Bernie Sanders has strongly criticized the nation’s “corrupt” political and economic system for threatening the country’s democracy and destroying the middle class.

“Our country today faces a series of unprecedented crises,” Sanders said during the first Democratic presidential debate of this year held on Tuesday in Las Vegas, Nevada.

“The middle class of this country for the last 40 years has been disappearing, millions of Americans are working longer hours for lower wages and yet almost all of the new income and wealth being created is going to the top 1 percent,” the independent senator from Vermont said.

“As a result of this disastrous Citizens United Supreme Court decision, our campaign finance system is corrupt and is undermining American democracy," he warned.

Sanders was referring to the US Supreme Court ruling in 2010, known as Citizens United, that allowed unlimited independent spending by corporations in elections.

Sanders also said that Wall Street, a term used to describe the US financial sector, has more power than lawmakers when it comes to setting financial regulations.

“Congress does not regulate Wall Street, Wall Street regulates Congress,” Sanders said in response to a comment made by leading Democratic presidential candidate Hillary Clinton, who was echoing Sanders’ criticism of Wall Street.

The two candidates made the exchange as they discussed their approach to growing US inequality and aiding the middle class, with both arguing that their policies would be tougher on Wall Street and the large banks.

Sanders’ emphasis on US income inequality and influence of corporate money on elections and government has helped him attract large crowds on the campaign trail.

But Clinton still leads the Democratic presidential field, with 45 percent of likely Democratic primary voters supporting her while 25 percent support Sanders, according to a new Fox News poll.