WASHINGTON - The U.S. ambassadorship to South Korea is set to stay open a while longer after the Trump administration dropped from consideration a prominent Washington-based academic who had been tapped for the job. The high-profile position has remained vacant for the past year as tensions with nuclear-armed North Korea have soared.

U.S. officials confirmed the withdrawal of Victor Cha, but did not spell out the reasons for it and who might be in the running to take his place.

The Washington Post reported Tuesday that Cha had privately expressed disagreement in late December with the Trump administration's policy on North Korea and on a U.S.-South Korea trade pact that Trump has threatened to scrap. The report also cited anonymous sources as saying there had been a problem with Cha's security clearance.

Hours later, Cha wrote in a commentary in the Post that he had voiced opposition to those within the administration who he said were suggesting military action against North Korea. Some have referred to it as a "bloody nose" strike that is intended to demonstrate U.S. resolve without provoking a wider war.

"North Korea, if not stopped, will build an arsenal with multiple nuclear missiles meant to threaten the U.S. homeland and blackmail us into abandoning our allies in Asia," wrote Cha, who served as director for Asian affairs on the National Security Council during the George W. Bush administration.

"But the answer is not, as some Trump administration officials have suggested, a preventive military strike," he said, warning that could put thousands of Americans at risk in South Korea and start a nuclear war.

In his State of the Union address on Tuesday, President Donald Trump said North Korea's "reckless pursuit of nuclear missiles could very soon threaten our homeland." He said the U.S. was waging a "maximum pressure" campaign to prevent that — referring to the international effort to deepen the North's economic and diplomatic isolation through sanctions.

The withdrawal of Cha's selection is particularly unusual as Washington had informed its close ally in Seoul of its intent to nominate him as ambassador, a position that requires Senate confirmation.

"It's a lengthy and thorough vetting process. Until a candidate is nominated, we have a highly experienced and well-respected charge d'affaires serving in Seoul," said White House spokeswoman Lindsay Walters.

Congressional Democrats criticized the move.

Sen. Tammy Duckworth of Illinois said: "We have reached a point where opposing war as the first resort seems to be a disqualifier from serving as ambassador." Sen. Edward Markey of Massachusetts warned: "The bloody nose strike contemplated by the Trump administration could lead to a catastrophic loss of life."

Cha, who is Korean-American, is the author of books on North Korea. During the Bush administration, he conducted nuclear negotiations with Pyongyang. He currently holds senior positions at the School of Foreign Service at Georgetown University and the Center for Strategic and International Studies think-tank .

The previous ambassador, Mark Lippert, was a political appointee of President Barack Obama and vacated the post as soon as Trump took office. The embassy in Seoul is currently led by the charge d'affaires, Marc Knapper, a career diplomat.

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Associated Press writer Catherine Lucey contributed to this report.

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