Muir asks Trump: Where was 'breakdown' in what US knew about COVID-19 spread?

During his exclusive interview with President Donald Trump in Arizona, ABC News anchor David Muir asked the commander in chief to clarify whether, a month after stopping travel from China to the U.S., he actually believed that the spread of novel coronavirus would end at 15 cases.

In late February, Trump said that the U.S. had gone from 15 to near zero.

"We're going very substantially down, not up. Going very substantially down. Schools should be preparing. Get ready just in case. The words are 'Just in case.' We don't think we'll be there. We don't think we'll be anywhere close,'" Trump said during a news conference on Feb. 26. "When you have 15 people and the 15 within a couple days is going to be down to close to zero, that's a pretty good job we've done."

Since the first cases were detected in China in December, the United States has become the worst-affected country, with more than 1.2 million diagnosed cases and at least 72,000 deaths, according to data from Johns Hopkins University.

Trump told Muir during Tuesday's interview that the cases had "mushroomed."

"There was a time when we had one person in this country. We knew about it. We worked on it. But we have one person, it mushroomed. ... Other people were coming in, also from Europe," Trump told the "World News Tonight" anchor.

Muir pushed back, however, reminding Trump that the U.S. had reached more than 1 million cases of novel coronavirus.

"You know why we’re at a million cases? Because we have more testing than anybody else. If we tested as much as these countries down here, OK, who don't do very much testing at all," Trump said.

"But you understand there's a huge disparity between 15 and more than a million cases. ... Was it an intelligence failure? Where was the breakdown that we, didn't know the scope of this?" Muir asked.

Trump did not answer Muir's question, but said that he'd closed the U.S. border.

"I was the only one that wanted to do it. And we had professionals, we had doctors, David, I was the only one that wanted to do it. And if I didn't do that -- Dr. [Anthony] Fauci said this -- we would have lost thousands and thousands, tens of thousands more lives, but I banned China, which is the primary source, from coming in. Then, not too long after that, I banned Europe because we saw what was going over -- what was happening in Europe. ... I think we did a phenomenal job," he said.

Tune into ABC at 1 p.m. ET and ABC News Live at 4 p.m. ET every weekday for special coverage of the novel coronavirus with the full ABC News team, including the latest news, context and analysis.