The White House has tapped former State Department adviser Victor Cha as the next U.S. ambassador to Korea, diplomatic sources said last week.

Cha is Korea chair at the Center for Strategic and International Studies and a professor at Georgetown University.

A senior State Department official confirmed the news, saying Cha is the most likely candidate for the post. But Cha said he has heard nothing officially from the White House, and understands that no decision has been made.

The post has been vacant since the last ambassador, Obama protégé Mark Lippert, left abruptly after the election of Donald Trump to the presidency. Deputy Chief of Mission Marc Knapper is working as chargé d'affaires.

Cha has also been mentioned as a candidate for assistant secretary of state for East Asian and Pacific affairs due to his experience as a former director for Asian affairs in the National Security Council under George W. Bush.

But Trump is having trouble filling senior posts in his erratic administration. Jon Huntsman, the former ambassador to China, has been selected as the new ambassador to Russia. He accepted the offer and already did the paperwork in April, but his nomination has not been made official yet.

Word is going round diplomatic circles in Washington that candidates have to pass a "loyalty test" to feed Trump's ego, and several candidates have failed at this last hurdle.

Former Governor of Iowa Terry Branstad, who has known Chinese President Xi Jinping personally for 30 years, was confirmed by the Senate as the new ambassador to Beijing in May. And banker William Hagerty was confirmed as the new ambassador to Japan.

