Heather Nauert, the State Department spokeswoman and one of the US's highest-ranking diplomats, was critical of former Secretary of State Rex Tillerson's refusal to deny reports that he called Trump a "moron" last year.

was critical of former Secretary of State Rex Tillerson's refusal to deny reports that he called Trump a "moron" last year. "Goodness, at this point just answer the question and kill this story," Nauert wrote in an October 15, 2017, email to her colleague.

Trump has reportedly asked Nauert to replace Nikki Haley as the US's ambassador to the UN.

Heather Nauert, the State Department spokeswoman whom President Donald Trump is expected to nominate to be the next US ambassador to the United Nations, was critical of former Secretary of State Rex Tillerson's refusal to address October 2017 reports that he privately called Trump a "moron" during a Pentagon meeting.

In one email to her State Department colleague obtained by Business Insider, Nauert expressed frustration over Tillerson's handling of the issue, arguing that he should "just answer the question and kill this story."

Nauert's former boss called questions about his alleged disparagement of the president "petty nonsense," refusing to directly knock down the reports. But he did respond to Republican Sen. Bob Corker's remark that Trump had "publicly castrated" him with tweets apparently undermining his diplomatic efforts, quipping to CNN's Jake Tapper, "I've checked. I'm intact."

At the same time, Tillerson denied reports that he considered resigning from his post and that Vice President Mike Pence had to persuade him to stay on.

"Bad — it's petty nonsense regarding moron but not castration?! Goodness, at this point just answer the question and kill this story," Nauert wrote in an October 15, 2017, email to Robert Greenan, the State Department's director of press operations, referring to a Politico story published that day detailing Tillerson's dodge.

Eleven days prior, Nauert publicly denied that Tillerson ever called the president a "moron."

"The secretary does not use that type of language, the secretary did not use that type of language to speak about the president of the United States," Nauert said during an October 4 press briefing.

In a February 3, 2018 email, Nauert again appeared frustrated with Tillerson. In a message to former White House communications director Hope Hicks, Nauert wrote, "Sorry about all of this. LMK if you need anything," in reference to a news report concerning Trump and Tillerson's differing messages on border protection.

Nauert and Greenan did not immediately respond to a request for comment.

The emails were obtained as a result of a Freedom of Information Act lawsuit filed by the nonpartisan non-profit government watchdog group Democracy Forward, which requested information regarding Tillerson's reported disparagement of the president. The original FOIA request was filed in October 2017, and the group filed a lawsuit in March 2018 after the government declined to release any responsive records. The emails were released to Democracy Forward late last month.

A complicated relationship

Nauert's emails illustrate the difficult relationship she had with Tillerson, who excluded his spokeswoman from meetings, rarely afforded her one-on-one time, and did not invite her on his international trips.

A senior State Department official, who requested anonymity to avoid jeopardizing relations with coworkers, recently told Business Insider that Tillerson "completely shut [Nauert] out," adding that she was viewed "as a spy for the White House." Nauert, who maintained the trust of the White House throughout, reportedly considered resigning on multiple occasions.

Nauert appears to have a close working relationship with Tillerson's replacement, former CIA director Mike Pompeo, with whom she travels extensively.

Read more: How Heather Nauert's unlikely rise at the State Department has made her a top contender for White House press secretary

Senior administration officials told multiple news outlets on Thursday that Trump has asked Nauert to replace UN ambassador Nikki Haley, who announced last month that she'll leave her post by the end of the year.

"She's under very serious consideration. She's excellent," Trump told reporters on Thursday of Nauert. "She's been a supporter a long time."

Nauert, 48, has for months balanced two high-profile positions at the State Department. Unlike most of her predecessors in both roles, Nauert, a former Fox News host, arrived in Washington last year without formal experience in foreign policy, government, or politics.