The first lady was campaigning in Phoenix, where in recent weeks Clinton has narrowed Trump’s lead and turned the traditionally Republican state into a tossup.

Obama said Trump’s statement represented a threat to “the very idea of America itself,” and argued that his repeated claims that the election is “rigged” was an effort by his campaign to stoke voter apathy and keep voters away from the polls.

“For the record, our democracy is revered around the world, and free elections are the best way on Earth to choose our leaders. This is how we elected John F. Kennedy, Ronald Reagan, two George Bushes and Barack Obama. It has worked for decades,” she said. “We are fortunate, and I have traveled the world, we are fortunate to live in a country where the voters decide our elections, where the voters decide who wins or loses. Period. End of story. And when a presidential candidate threatens to ignore our voices and reject the outcome of the election, he is threatening the very idea of America itself.”

Without even having to mention Trump by name, Obama has repeatedly given some of the most stirring arguments for Clinton and against Trump, often using the businessman’s statements against him.

Campaigning in New Hampshire last week, Obama delivered a powerful denouncement of Trump’s history of demeaning women, which quickly went viral.

In her remarks on Thursday, Obama said her office was inundated with responses to the speech, in which she spoke in personal terms about how the 2005 video of Trump bragging about sexual assault had “shaken me to my core.”

But she urged Clinton supporters to use her words to rally voters.

“Don’t just tweet about my speech,” she said. “If you liked my speech last week, go vote!”

Obama attacked Trump’s divisiveness, saying that his propensity to insult and denigrate groups, from immigrants to veterans, from women to the disabled, from Muslims to African Americans, stems from his background as a wealthy real estate mogul.