During a campaign rally in Lake Worth, Florida, on Wednesday, Hillary Clinton hammered Donald Trump’s refusal to say he will accept the results of the November election, arguing that he is undermining democratic values in the United States.

Clinton called Trump’s failure to commit to accepting election results “horrifying,” and questioned whether Trump has read the U.S. Constitution.

“When you are sworn in as president, you take an oath. You take an oath to preserve, protect and defend the Constitution. And listening to Donald Trump’s campaign, I truly doubt that he has ever read the Constitution,” she said. “Or if he did back in school, he certainly doesn’t remember it, and he doesn’t understand — it is the most important founding document for the longest-lasting, greatest democracy in the history of the world.”

Clinton said that America’s commitment to free elections “is one of the things that makes America who we are.”

“We fool around with that and we criticize that at our peril,” she told the crowd. “We can never tolerate anyone running to be president of the United States who undermines and questions our fundamental democratic values.”

Clinton listed the many groups Trump has insulted on the campaign trail, including Muslims and women, before saying, “But now his final target is democracy itself.”

The former secretary of state then recalled American history and noted that America has “faced challenges to our democracy before.” She said that President George Washington’s refusal to become king after serving as president was “one of the most important decisions in our history.”

“We had a revolution to get out from under one king, and George Washington was wise enough to say, ‘No, I’m going home. We need to have the peaceful transfer of power,'” Clinton said. “One person can’t act like they’re in charge of everything in America. That’s not who we are.”

She quipped that Trump would probably call George Washington a “loser.”