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.
Mr. Cha, a professor at Georgetown University and senior adviser at the Center for Strategic and International Studies, did not respond to a request for comment. The Washington Post first reported that the White House was not moving forward with his nomination.
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The White House had initially hoped to have a new ambassador in place in time for the Winter Olympic Games in Pyeongchang, South Korea, which begin next Friday. 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.
“This is 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,” said Michael J. Green, a colleague of Mr. Cha.
Unlike many other Republican foreign policy experts, Mr. Cha did not sign a letter critical of Mr. Trump during the 2016 presidential campaign. He has been circumspect, even in private settings, about commenting on the administration’s North Korea policy.
During the Bush administration, Mr. Cha conducted multilateral negotiations with North Korea as part of the so-called six-party process. An American-born son of South Korean immigrants, Mr. Cha has told friends about how he once feigned being unable to speak or understand Korean and then listened to his North Korean counterparts as they discussed negotiating tactics across the table.
Mr. Cha is hardly alone in questioning the wisdom of a preventive military strike on North Korea.
In testimony on Tuesday before the Senate Armed Services Committee, Dennis C. Blair, a former director of national intelligence in the Obama administration and Navy admiral who also led the United States Pacific Command, disputed the contention that the United States could neither contain a nuclear North Korea, nor had no choice but to launch a military attack.
Mr. Green, who also served in Bush administration, testified at the same hearing that even a limited strike would almost certainly provoke a catastrophic retaliation by the North.
“We have not tested that proposition since the Korean War, and most North Korea analysts would tell you that Kim Jong-un would have to strike back,” Mr. Green said. “Escalation to nuclear, biological or chemical weapons by the North would mean a conflict that goes from tens of thousands killed to millions.”