President Trump and South Korean President Moon Jae-in talk during a dinner in the State Dining Room of the White House on June 29. The two leaders will meet again in New York on Thursday amid growing concerns over the threat posed by North Korea. (Jabin Botsford/The Washington Post)

President Trump and his top aides say they're doing everything in their power to pursue a diplomatic and peaceful resolution to the North Korea nuclear threat. But eight months into Trump's tenure, he has yet to nominate a U.S. ambassador to South Korea, a glaring omission as the White House tries to formulate a coherent policy to confront Pyongyang.

The vacancy has left President Moon Jae-in's new government without a prestigious and powerful partner from the Trump administration on the ground in Seoul at a time of escalating anxiety in East Asia — and without someone to help decode the president's rhetorical bombast. On Tuesday, Trump threatened during a speech at the United Nations to "totally destroy" North Korea if necessary.

“The North Korea issue is such a high priority that it is imperative there is coordination between the United States and South Korea, and there needs to be a rock-solid channel of communication,” said Scott Snyder, director of the U.S.-Korea policy program at the Council on Foreign Relations. “That is simply absent.”

In some ways, Trump and his White House aides are personally compensating for that absence. On Thursday, Trump will meet separately with Moon and Japanese Prime Minister Shinzo Abe on the sidelines of the U.N. General Assembly. The three leaders also will hold a trilateral discussion on North Korea’s nuclear and ballistic missile programs, the second time the three have done so during Trump’s tenure.

Moon, who took office in May after Park Geun-hye resigned in scandal, also met with Trump at the White House in June for two days of meetings, including a working dinner.

But behind the scenes, Korea watchers in Washington say they are perplexed about the lengthy delay in filling the State Department's top Seoul post. Since the spring, the leading — and perhaps only — candidate said to be in consideration has been Victor D. Cha, a former George W. Bush administration Asia policy aide who is the Korea chair at the Center for Strategic and International Studies.

Cha is purportedly undergoing a standard vetting by the White House, including a background check and examination of his finances. If Trump were to nominate him, Cha’s appointment would be subject to Senate approval.

Cha, a frequent commentator on Asia policy, did not respond to requests for comment. Associates suggested the White House has instructed him to “go dark” as the final stages of the vetting process are completed.

But one acquaintance said Cha was told his nomination was unlikely to happen before November or December.

“We have nothing to announce at this time,” a senior Trump administration official said Wednesday when asked about the South Korean job. “We are very focused on identifying the right person for this crucial position.”

The official, who was not authorized to speak on the record, said the administration is being well-served by Marc Knapper, a career State Department official who was elevated from deputy chief of mission at the embassy in Seoul to chargé d’affaires after Trump was sworn in.

Knapper, who served as deputy chief for two years, speaks fluent Korean and is said to be well-respected in Seoul.

The situation stands in contrast to the scenario in Japan and China where William Hagerty, a Tennessee businessman and Terry Branstad, the former Iowa governor, have been in place for several months.

“An ambassador has more prestige than a seat-warmer and more power,” said David Kang, director of the Korean Studies Institute at the University of Southern California. “An ambassador speaks with a lot more authority and more influence in Korea and the United States. This stuff is really important in trying to get countries to coordinate and listen to each other.”

Under Obama, Mark Lippert, a longtime aide who worked on his campaign and in the White House, served as the ambassador to South Korea from 2014-2017.

In addition to the North Korea crisis, the U.S.-South Korea relationship has been strained over Trump's announcement that his administration will seek to renegotiate a bilateral trade deal signed by Obama in 2011. And Moon alarmed Washington during his campaign by questioning South Korea's commitment to the installation of the U.S.-backed THAAD missile defense program, though he has since agreed to allow the costly initiative, strenuously opposed by Beijing, to go forward.

Moon has signaled an openness to engagement with the North that conflicts with the harder-line positions of Washington and Tokyo. Cha is considered to be relatively hawkish on North Korea.

Foreign policy analysts who have been in touch with White House officials said the Trump administration has been slow to nominate officials at State in part because Trump aides are refusing to consider the dozens of national security experts who signed a pair of "never Trump" public letters during the campaign.

That significantly narrowed the pool of candidates and bottled up the nomination process as Trump aides — including senior adviser Jared Kushner, Trump’s son-in-law, and Stephen K. Bannon, the former White House chief strategist who stepped down last month — carefully vetted each name that was suggested inside the West Wing.

The Cha candidacy is said to be slowly working its way through the process. In the meantime, some in Washington fear the lengthy vacancy in Seoul has sent a message that will be difficult to overcome: that Trump’s White House doesn’t really care about what an ambassador on the ground 35 miles from the North Korean border has to say about policy.

The delay suggests “that this administration has a reckless indifference,” said a former Obama administration official who spoke on the condition of anonymity to speak frankly. “They’re not big on consultation and not looking for advice. This is a president who makes up his own mind.”