Clinton asked voters to imagine "two different Americas," one where she wins the election and one where Donald Trump becomes president.
"Just for the sake of this exercise, imagine it's Donald Trump standing in front of the Capitol," Clinton said. "We already know a lot about him."
She cited Trump's comments about women, people with disabilities, black and Latino voters, Muslims, and immigrants.
Trump "pits people against each other instead of pulling us together," Clinton said.
She asked voters to imagine Trump with the ability to order a nuclear strike.
"Think about what it would mean to entrust the nuclear codes to someone with a very thin skin, who lashes out at anyone who challenges him. Imagine how easily it could be that Donald Trump would feel insulted and start a real war, not just a Twitter war, at 3 o'clock in the morning."
She also slammed Trump for his business practices, saying that he "built his career exploiting workers, stiffing small businesses."
"Everywhere he goes, he leaves people behind," Clinton said.
She told voters to "stage an intervention" if they know anybody planning to vote for Trump.
"Sit down with them and ask them what they care about and if they say they're just frustrated or angry, say you understand, but anger is not a plan," Clinton said.