Trump was claiming that criminals were sent to the U.S. without documentation to fill American jails when the lights went dark.
"Oh, I like that much better," he said when the stage lights went out. "Those lights were brutal. Did they come from the dishonest press?"
Trump suggested the venue would save on electricity if they left the lights off. When the lights were turned back on, he led the crowd in a chant.
"Turn off the lights, turn off the lights," Trump chanted.
He later told the crowd a protester killed the lights.
Watch his chant, via CNN: