With the State Department still grappling with numerous vacancies at top posts, one of America's most senior diplomats is stepping down and the White House has rescinded its pick for Ambassador of South Korea.

The U.S. has not had an Ambassador to South Korea for over year. The administration's expected nominee for the position, Victor Cha, was withdrawn this week, in large part due to his opposition to small-scale strikes against North Korea. National Security Adviser H.R. McMaster has pushed for such a "bloody nose" strike against the North Korean regime to punish it for its nuclear provocations.

Vice President Mike Pence is expected to visit South Korea later this month for the Winter Olympics. When he does, there will be no American ambassador to meet him and give him the lay of the land.

Forty-one U.S. ambassador posts are currently vacant, and there are no American ambassadors to Middle East hotspots like Egypt, Jordan, Saudi Arabia, and Turkey.

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In its first year, the Trump administration nominated 24 senior officials at the State Department and 64 ambassadors. But that's still 37 percent fewer senior official nominations than the Obama administration after its first year, and 31 percent fewer ambassador nominations, according to the American Foreign Service Association.

Ambassador Ronald Neumann told CBS News that he is more worried about the lack of leadership at the State Department than the number of ambassador vacancies.

"The much bigger question is the holes in Washington, the slowdown in producing policy guidance," Neumann, now the President of the American Academy of Diplomacy, explained. "If you only confirm political appointees your overall message is that you don't trust the foreign service."

Another hole opened up on Thursday when Under Secretary of State for Political Affairs Thomas Shannon announced his retirement. Shannon, a career foreign service officer with expertise in South America and Africa, had told Secretary of State Rex Tillerson keep his job for one year in the new administration. He has now agreed to maintain on the job until a replacement is identified.

The 60-year old diplomat leaves big shoes to fill. Tillerson has called him a "walking encyclopedia," according to Under Secretary Steve Goldstein. Shannon's wealth of knowledge helped guide Tillerson during his first year as America's chief diplomat. Shannon, who served six presidents and ten secretaries of State, has also taken a leading roll in dealing with Venezuela and Russia over the past year. Shannon met with Russia's new ambassador to the U.S. in December and had a meeting with Russia's Deputy Foreign Minister in September.

Shannon is also popular among families of Americans detained abroad, such as the family of Josh Holt, who has been held in Venezuela for more than a year. When Shannon met with Holt's family, he gave them his personal contact info.

Goldstein denied that Shannon's decision to leave had anything to do with the low morale at the department.

"The combination of the Under Secretary turning 60, 35 years of service, the death of his mother, and his commitment to the secretary that he would stay a year - all of those were factors," said Goldstein. He added that inferring anything else from Shannon's departure would be "wrong."

Yet State Department veterans worry about Shannon leaving a void that won't be easily filled due to the lack of sernior leadership at the department already.

"Ambassador Tom Shannon a stellar diplomat. His resignation a real loss. The Trump Administration has decimated the Foreign Service and now needs to make things right," wrote former State Department Under Secretary Nicholas Burns on twitter.