Donovan Slack | USA TODAY

In a radio ad urging South Carolina to “wake up!” director Spike Lee says Bernie Sanders will “do the right thing” if he is elected.

“How can we be sure? Bernie was at the March on Washington with Dr. King, he was arrested in Chicago for protesting segregation at public schools,” Lee says in the one-minute spot. “He fought for wealth and education equality throughout his whole career. No flipping, no flopping. Enough talk. Time for action.”

The Sanders campaign rolled out the new ad Tuesday, four days before the Democratic primary in South Carolina, in which black voters are expected to play a key role. Recent polls show Clinton with a whopping lead over Sanders in the state, 57%-33% on average, according to RealClearPolitics.

In the ad, Lee also highlights Sanders’ reliance on small-dollar donors.

“I know that you know the system is rigged,” he said. “Ninety-nine percent of Americans were hurt by the great recession of 2008 and many are still recovering, and that’s why I’m officially endorsing my brother Bernie sanders. Bernie takes no money from corporations – nada — which means he is not on the take.”