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.

Image Victor D. Cha will not be the American ambassador to Seoul. Credit... Yonhap, via European Pressphoto Agency

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.