Bolton, who was ousted earlier this month after a year and a half as Trump’s top security aide in part because of his hawkishness, began his remarks by joking that North Korea’s leadership was likely “delighted” by the fact he was there in a private capacity.

“Perhaps they’ll be a little less delighted now that I can speak in unvarnished terms about the grave and growing threat that the North Korean nuclear weapons program poses to international peace and security," he added.

Bolton alluded to several of the policy disagreements he had with his former boss, most notably that Kim was not ready to give up his nuclear weapons program, as Trump has frequently insisted after a handful of meetings with the reclusive leader.

Trump has so far held two summits with Kim, and has teased the possibility of a third before next year’s election. Neither meeting has yielded any concrete progress toward a deal, with North Korea suggesting that it would like to see relief from sanctions before taking any steps to denuclearize.

He also appeared to ridicule Trump’s fixation on the spectacle of meeting with Kim, arguing that even a partial agreement would disproportionately benefit North Korea.

“They want a piece of something that we should not be prepared to give them,” Bolton said.

After outlining several paths toward diplomacy — including “limited” regime change and military force — that have a slim chance of coming to fruition under Trump, Bolton asserted that one of the consequences of letting North Korea go unchecked was that they could become “the Walmart or the Amazon of deliverable nuclear weapons.”

“These are questions that need to focus our attention, not can we get another summit with Kim Jong Un or what the state of staff-level negotiations are to achieve a commitment from North Korea it will never honor,” he continued.

Bolton also doubled down on calls to implement a “Libya model” when dealing with North Korea, comments that Trump derisively cited as detrimental to U.S.-North Korea relations after Bolton’s exit. And Bolton countered Trump’s repeated assertions that the U.S. is in “no rush” to push Kim to wind down his nuclear programs while taking an indirect shot at his former boss for his lackadaisical attitude toward recent short-range missile tests in North Korea.

While Trump has said those tests were not a violation of U.N. Security Council resolutions, Bolton on Monday sided with anxious U.S. allies like Japan and South Korea in declaring that they were. Moreover, he added, Trump’s apparent disregard for the resolutions undermines U.S. policy by giving off the message that its leadership doesn’t care about the sanctions in those or other U.N. resolutions.

“When you ask for consistent behavior from others, you have to demonstrate it yourself and when we fail to do that we open ourselves — and our policy — to failure,” Bolton warned.

In defending his leniency about the short-range tests, which have alarmed allies, Trump has said they are preferable to testing intercontinental ballistic missiles or conducting other kinds of nuclear tests. But Bolton cautioned against complacency because of this switch, contending that it “tells us nothing about either North Korea’s intention or its strategy as it’s playing out.”

One potential and “very troubling” reason behind the switch, he suggested, “is that North Korea has, in its judgment, for well or ill, finished testing and can produce nuclear warheads and long range ballistic missiles.”

Bolton didn't disagree with Trump across the board, noting that he too wanted "better burden sharing" from U.S. allies especially in the context of NATO. But "this is not the time for U.S. disengagement and withdrawal. This is the time for more U.S. involvement and leadership on the Korean peninsula, in Asia and worldwide," he concluded. "More, not less."