“We are waging a campaign of maximum pressure to prevent that from happening,” he said. “Past experience has taught us that complacency and concessions only invite aggression and provocation. I will not repeat the mistakes of past administrations that got us into this dangerous position.”
Mr. Trump did not, as he has before, issue specific threats of a military strike on the North. But he outlined an unrelenting case for what he called the North Korean government’s “depraved character,” echoing a speech he delivered to the South Korean National Assembly in Seoul in November.
The president drew on the stories of two victims of North Korean cruelty: an American college student, Otto F. Warmbier, who fell into an irreversible coma while in detention in Pyongyang, the capital, and later died; and a North Korean man who lost his leg while searching for food for his starving family. He later defected.
Gesturing to Mr. Warmbier’s parents, Fred and Cindy, who watched from the visitors’ gallery in the House, their eyes wet with tears, Mr. Trump said, “You are powerful witnesses to a menace that threatens our world, and your strength truly inspires us all.”
The defector, Ji Seong-ho, was also in the gallery and held up his wooden crutches in triumph when Mr. Trump hailed him.
Hours before the speech, the president’s Korea policy was buffeted by the administration’s decision to abandon a long-delayed plan to nominate a prominent Korea scholar, Victor D. Cha, as its ambassador to Seoul.
Mr. Cha, 57, had voiced opposition to the administration’s threat to carry out a preventive military strike against North Korea, said two people with knowledge of the decision. He had already undergone an extensive vetting process, and his name had been submitted for approval to the South Korean government — normally an indication that the background check was complete.
Officials in Seoul had already signed off on the ambassadorship; Mr. Cha is a Republican who identifies as a hawk on North Korea. But friends said he told Pentagon and other administration officials his concerns about ordering a pre-emptive, or preventive, military strike on North Korea before it had the capacity to fire a nuclear-armed missile at the United States.
Administration officials, particularly the White House national security adviser, Lt. Gen. H. R. McMaster, have raised the prospect of such a strike — sometimes called the “bloody nose” strategy — though they emphasize they would prefer to solve the confrontation with Pyongyang through diplomacy.
Mr. Cha has also publicly voiced the high cost to both Washington and Seoul of ripping up the Korea Free Trade Agreement, as Mr. Trump has threatened to do, unless the South Koreans agree to renegotiate the deal.
The White House declined to comment Tuesday on the reasons for its decision, though a senior official played down policy disagreements as the cause. The administration had not formally submitted Mr. Cha’s name to the Senate, even after he had undergone months of vetting.
The White House had initially hoped to have a new ambassador in place in time for the Winter Games, which begin in 10 days in the South Korean town of Pyeongchang. But as the deadline approached, Mr. Cha told friends he had heard nothing from the White House or the State Department about the status of his nomination. The Washington Post first reported that the White House was not moving forward with his nomination.
Michael J. Green, a colleague of Mr. Cha, said the dropped ambassadorship was “discouraging in terms of what it says about the administration’s North Korea policy, but also their ability to attract qualified people to come into these kinds of jobs.”
In his speech, Mr. Trump made no mention of the Winter Olympic Games. Nor did he mention a budding détente between North and South Korea, which have agreed to march their teams into the opening ceremony under a single flag and to field a unified women’s ice hockey team.
For the president, cataloging the horrors inflicted by North Korea was part of an exercise that he called “restoring clarity about our adversaries.” He said he had stood up for antigovernment demonstrators in Iran and asked Congress to fix the flaws in the “terrible” nuclear deal that world powers brokered with the country in 2015.
The president also said the United States had imposed sanctions on Cuba and Venezuela, though he made no mention of new penalties against Russia, which lawmakers had passed in a lopsided majority but which the administration has so far declined to impose.
Mr. Trump said much less about America’s role in alliances like the North Atlantic Treaty Organization. And he barely mentioned China or Russia, two countries his own administration identified as the nation’s greatest geopolitical adversaries in the recent National Security Strategy.
While he mentioned his decision to recognize Jerusalem as the capital of Israel, Mr. Trump said nothing about his administration’s effort to broker a peace accord between Israel and the Palestinians. That effort seemed more elusive than ever, given Palestinian outrage over Jerusalem.
Rather than talk about peace, Mr. Trump emphasized his determination to punish countries that split with the United States over what he called “America’s sovereign right to make this recognition.”
“That is why, tonight, I am asking Congress to pass legislation to help insure American foreign-assistance dollars always serve American interests, and only go to America’s friends,” he said.