Fifteen years ago, as Hillary Clinton walked toward the still-burning pile of rubble that was formerly the World Trade Center, a mask over her face and fellow top New York politicians by her side, she could think of just one word to describe it: "hell."

"There was this curtain of black smoke that stretched across the island, basically," Clinton recalled in a wide-ranging interview with CNN's Chris Cuomo that aired Sunday, the 15th anniversary of the 9/11 attacks. "Occasionally it would be broken by a firefighter coming out. I remember one image so indelibly, dragging his ax. It was as close to a depiction of hell that I've ever personally seen ... The loss of life was so overwhelming."

Throughout her presidential campaign, Clinton has often talked about what it was like to be a U.S. senator from New York during the 9/11 attacks and how she personally lobbied President George W. Bush to get $20 billion in aid for New York.

"It was a great moment of national unity," she told Cuomo.

And probably a stark contrast to today's divisive presidential campaign. The interview was taped before Clinton told donors in New York on Friday that "half" of Donald Trump's supporters could fit in a "basket of deplorables," a comment the Trump campaign seized on and one she said Saturday that she regretted.

On Sunday, both Clinton and Trump attended a 9/11 memorial ceremony at Ground Zero. Clinton left the ceremony early after her campaign said she was "overheated."

In her interview with Cuomo, Clinton didn't shy away from attacking her opponent on foreign policy. She called Trump's projection of strength "phony."

"Well, there's phony strength and there's real strength," Clinton said in a response to a question about whether people gravitate toward Trump because of his perceived strength. "And it's phony strength to not know what you're talking about and to make outrageous statements that will make our job harder. Real strength is leveling with the American people."

She said Trump is "conveying several perceptions around the world that are quite damaging." She had strong words for his praising of authoritarian leaders, including former Iraqi president Saddam Hussein and Russian President Vladimir Putin, for example, saying it sets a tone that America is willing to give a pass to aggressive behavior. And she said his controversial comments about Muslims — such as his proposal to temporarily ban them from the United States — "plays right into" the hands of the Islamic State militant group.

"We're going to have to undo the damage he's already done in this campaign," Clinton said.