Wess Mitchell’s resignation adds to the exodus of senior officials who have championed Nato in the face of Trump’s reported desire to withdraw

The state department’s top diplomat dealing with Europe, and an outspoken supporter of Nato, has announced his resignation.

Wess Mitchell said he was leaving for personal reasons, after just 16 months in the job as assistant secretary of state for European and Eurasian affairs, adding that he was “fully supportive” of the US secretary of state, Mike Pompeo.

But the resignation adds to the exodus of senior officials who have championed the Nato alliance in the face of Donald Trump’s reported desire to withdraw. Mitchell also oversaw relations with the European Union, which the president has relentlessly berated.

Pompeo emphasised the importance of “sturdy alliances” and “beautiful coalitions” to US security in remarks delivered on Tuesday, but he also praised the “new winds” of populism across the world, embodied by Brexit and the rise of Trump, the Five Star movement in Italy, and Mahathir Mohamad in Malaysia. He also included Emmanuel Macron in France.

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“New winds are blowing across the world,” the US secretary of state told the World Economic Forum in Davos. His remarks were delivered by video as the US administration delegation canceled its trip to Switzerland because of the continuing government shutdown.

“I would argue that this disruption is a positive development,” Pompeo said. “We are embracing time-tested truths. Truths like this: nations matter. No international body can stand up for a people as well as their own leaders can.”

Ivo Daalder, who was US ambassador to Nato in the Obama administration, said: “Just having been in Europe, there is a deep disquiet among our allies about America’s continued commitment to Europe, including Nato.

“Having the top diplomat responsible for Europe step down only adds to the uncertainty and concern among all of our allies,” Daalder added.

The former defence secretary, James Mattis, resigned in December, pointing to the need to maintain strong alliances and respect allies as his central difference with Trump. Two other senior Pentagon officials in charge of ties with Nato stepped down in late 2018: Thomas Goffus, deputy assistant defence secretary for Europe and Nato policy, and Robert Karem, assistant defence secretary for international security affairs.

A Democratic staffer in the Senate said Mitchell’s departure was “unfortunate for those of us who want a responsible Russia policy”.

“I’m surprised he lasted as long as he did,” the staffer said. “He was much more forward leaning than the White House on Russia and never seemed to be a Trump worshipper like so many in the administration.”

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“This is surprising news, which seems to have caught everyone off guard,” said Amanda Sloat, a former senior state department official. “He doesn’t appear to have shared this news with his ambassadors, who were in Washington last week for a global chiefs of mission conference. His deputy is also slated to retire soon, which raises question of near-term leadership on European policy at a time of challenges there.”

In an interview with the Washington Post, which broke the news of his resignation, Mitchell said: “I feel like I’ve done what I came in to do. My kids have a greater claim to my time right now than the public does.”

Mitchell calls himself a devoted Atlanticist and insisted that “nothing could be further from the truth” that US membership of Nato was in question.

Mitchell was instrumental in promoting a friendlier US policy towards Viktor Orbán, Hungary’s rightwing prime minister, and also helped broker a settlement with Greece over Macedonia’s name.

“Wess has been one of the pillars of this administration’s most constructive foreign policy ideas,” said Daniel Fried, who did the same Europe assistant secretary job at state department in the George W Bush administration. “He has generated wide respect in Europe and his loss will be felt.”

“Mitchell was a strong supporter of Nato, particularly in eastern Europe, where he will be sorely missed,” said Thomas Wright, the director of the Centre on the US and Europe at the Brookings Institution. “His departure follows the resignation of senior Pentagon officials – Robert Karem and Tom Goffus – working on Nato along with Secretary Mattis. Without this pro-alliance caucus, Nato is now more vulnerable than at any time since the beginning of the Trump administration.”