The sudden resignation of US Defence Secretary James Mattis sent shock waves worldwide yesterday, reigniting concerns about the future of American alliances, now that a man regarded as a key stabilising influence in the Trump administration is departing.
The announcement that he would leave in February, coming amid similarly abrupt decisions by the US administration to withdraw troops from Syria and Afghanistan, was greeted with dismay from Europe to Asia.
German Foreign Minister Heiko Maas said: "(President Donald Trump's) decision could hurt the fight against the Islamic State (in Iraq and Syria) and endanger what has been achieved."
Mr Carl Bildt, co-chair of the European Council on Foreign Relations, added: "A morning of alarm in Europe. Mattis is the remaining strong bond across the Atlantic in the Trump administration."
US engagement is considered key to maintaining stability in Asian hot spots such as the Korean peninsula. Withdrawal from Syria, meanwhile, could leave a vacuum, enabling the resurgence of ISIS militants and be seen as an abandonment of America's Kurdish allies.
Israel, which favours an American presence that keeps pro-Iranian forces at bay in the region, is said to be miffed. "We will take care to maintain the security of Israel and to defend ourselves," Prime Minister Benjamin Netan-yahu said yesterday.
The Syrian Democratic Forces, a US ally in the Syrian battle which has a strong Kurdish contingent, said the move would have "dangerous implications".
In his resignation letter, Mr Mattis stressed the importance of treating US allies with respect and being clear-eyed about both malign actors and strategic competitors, and suggested that his views were at odds with the President's.
"One core belief I have always held is that our strength as a nation is inextricably linked to the strength of our unique and comprehensive system of alliances and partnerships. While the US remains the indispensable nation in the free world, we cannot protect our interests or serve that role effectively without maintaining strong alliances and showing respect to those allies," Mr Mattis wrote.
"Because you have the right to have a secretary of defence whose views are better aligned with yours... I believe it is right for me to step down from my position."
It is the first departure from the Trump White House explicitly attributed to a principled difference of opinion. The New York Times said the resignation letter was distributed by Mr Mattis' aides in the corridors of the White House on Thursday afternoon after he failed for the last time to persuade Mr Trump to reverse his decision on Syria.
Mr Trump's Syrian decision and his reported order to begin planning for the drawdown of American troops from Afghanistan have left him unusually isolated even among his own party.
Republican Senator Marco Rubio said the resignation letter "makes it abundantly clear that we are headed towards a series of grave policy errors which will endanger our nation, damage our alliances and empower our adversaries".
Senate Majority Leader Mitch McConnell said he was distressed to learn that Mr Mattis was resigning due to sharp differences with the President on key aspects of America's global leadership, such as strengthening alliances and having a clear-eyed understanding of its friends and foes.
"It is regrettable that the President must now choose a new secretary of defence. But I urge him to select a leader who shares Secretary Mattis' understanding of these vital principles and his total commitment to America's service members," Mr McConnell said.
Republican Senator Lindsey Graham, who has been close to Mr Trump, said: "This is chaos." He also said on Twitter that the move would be a "boost to ISIS".
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