The White House has formally announced its intention to nominate deputy national security adviser Kathleen Troia McFarland as ambassador to Singapore.
"I am pleased to nominate K.T. McFarland to be Ambassador to Singapore, one of America's great allies," President Donald Trump said in an announcement last Friday.
"While I am sorry to lose her, K.T's work in developing policies that put American interests first will have a lasting impact. She will remain an essential team member as she fulfils this new and important role."
Ms McFarland's appointment has to be confirmed by the Senate before it can take effect, a process that could take weeks.
The 65-year-old from Wisconsin began her career in the 1970s as a night shift secretary on Dr Henry Kissinger's staff. She went on to work in the Nixon, Ford and Reagan administrations, including in the National Security Council and Department of Defence. For a period, she was also a contributor to Fox News on security issues.
Ms McFarland is widely seen as having the President's ear. "She understands the President," a senior diplomat in Washington told The Sunday Times. "She would be able to articulate his strategic world view."
In an e-mail to The Sunday Times weeks ago, when reports first emerged that Ms McFarland was being considered for the Singapore post, Mr Frank Lavin, a former US ambassador to Singapore, said that she "certainly has policy depth" and "reach back in Washington".
Ms McFarland's boss, National Security Adviser H.R. McMaster, said in the White House announcement that she laid the foundation of the first strategic policy reviews that the National Security Council would continue to build upon. He added: "K.T. is leaving a great team in place to support the President, and our friends in Singapore know they are getting one of his top aides as their American ambassador."
In the Reagan administration, Ms McFarland worked as a speech writer to then Defence Secretary Caspar Weinberger. His 1984 Weinberger Doctrine, laying out guidelines for the circumstances in which the US should become involved in military operations overseas, finds echoes in the current administration's "peace through strength" approach.
At a Jan 10 conference on America's role in the world at the US Institute for Peace in Washington, Ms McFarland said: "We have a president who is going to seize this unique historic moment (and) is going to rebuild America's defences.
"Nobody's talking about giving up the things that have been part of America's post-war period, but maybe recalibrate them, see what other opportunities exist to strengthen them."
American values would "continue to be the bedrock, American global leadership is going to continue", she said. The US' alliance structures had "kept the peace for the longest time", she added.