"Today, I hope I speak not only for our countries, but for all civilized nations, when I say to the North: Do not underestimate us. And do not try us," Trump said. "We will defend our common security, our shared prosperity, and our sacred liberty," the president said to cheers.
The comments contrasted remarks the president made earlier in the week, in which he appeared open to possible talks with North Korean leader Kim Jong Un.
During a news conference with South Korean President Moon Jae-in on Tuesday, Trump argued that "it makes sense for North Korea to come to the table and make a deal that is good for the people of North Korea and for the world."
"I do see certain movement," Trump said.
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That tone matched his speech on Wednesday.
"The world cannot tolerate the menace of a rogue regime that threatens with nuclear devastation," Trump argued, while advocating for "peace through strength."
"All responsible nations must join forces to isolate the brutal regime of North Korea," he said.
"It is our responsibility and our duty to confront this danger together - because the longer we wait, the greater the danger grows, and the fewer the options become," he continued. "And to those nations that choose to ignore this threat or, worse still, to enable it: The weight of this crisis is on your conscience."
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