(Dec 21): Defense Secretary Jim Mattis announced his resignation on Thursday, citing differences over policy with Donald Trump, a day after the president abruptly called for the withdrawal of American forces from Syria.

Mattis informed the president of his decision in a meeting earlier in the afternoon in which the two discussed policy differences that have included the president’s decision to pull out of Syria, said a White House official. Mattis’s departure didn’t cause the president to rethink his decision on Syria, the official added.

In a two-page letter to the president, Mattis laid out his convictions on the value of US leadership in strategic alliances, including the North Atlantic Treaty Organization and the 74-nation coalition to defeat Islamic State. His letter also suggested differences with Trump over the president’s handling of the challenges from Russia and China.

“Because you have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects, I believe it is right for me to step down from my position,” Mattis said in the letter to Trump released by the Pentagon.

Moments earlier, Trump announced the news on Twitter, saying that Mattis would be the latest senior official to leave his Cabinet and that the former Marine general would be “retiring, with distinction, at the end of February.” Trump said he would name a new Pentagon chief “shortly.”

Republican Senator Marco Rubio said in a tweet Mattis’s 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 & empower our adversaries.”

“This is scary,” Senator Mark Warner, the top-ranking Democrat on the Intelligence Committee, said in a tweet posted shortly after the announcement. “Secretary Mattis has been an island of stability amidst the chaos of the Trump administration.”

Mattis was one of Trump’s first cabinet picks after the 2016 election. He was long seen as a force for stability in foreign policy in an administration that has had to manage crises from North Korea to Syria under a president who prides himself on his unpredictability. But like other senior national security advisers, he was believed to have pushed back on Trump’s decision this week to abruptly withdraw American troops from Syria.

After Trump said he’d nominate Mattis for the top Pentagon job, the late Senator John McCain hailed him as “one of the finest military officers of his generation and an extraordinary leader who inspires a rare and special admiration of his troops.” Short and wiry with a brush-cut haircut, Mattis was known as the “Warrior Monk” and sometimes as “Mad Dog,” a nickname he disliked as much as Trump loved invoking it.

At the Pentagon, he followed a succession of defence chiefs -- Ash Carter, Chuck Hagel and Leon Panetta -- who each lasted about two years in office.

Defence spending surge
Beyond his reputation as a voice for stability in military and foreign policy, Mattis may be best-remembered for overseeing a surge in defence spending. The fiscal year 2019 military budget of more than US$715 billion ($980 billion) bore his imprint and was seen as fulfillment of a key campaign pledge by Trump, ramping up spending for weapons systems including Lockheed Martin Corp.’s F-35 jet and new aircraft carriers built by Huntington Ingalls Inc.

“He managed to secure large budget increases for the Pentagon while simultaneously dissuading the president from withdrawing troops from the wars in Afghanistan, Iraq and Syria, as he advocated during his campaign, and in fact convinced him to step up efforts in these areas,” said Rob Levinson, a defense analyst with Bloomberg Government. “He sought to increase the Pentagon’s ‘lethality’ and tame its sprawling bureaucracy and associated costs, but the jury is still out on whether these efforts have made any real difference.”

Mattis found himself on the defensive after excerpts from author Bob Woodward’s book “Fear,” published in early September, painted the publicly taciturn Pentagon secretary as critical in private of the commander-in-chief.

According to Woodward, Mattis pushed back early in 2018 when Trump questioned the massive US military presence on the Korean peninsula, asking why the US was spending so much.

‘World War III’
“We’re doing this in order to prevent World War III,” Mattis said, according to the book. He went on to tell associates that the president had the understanding of a “fifth or sixth-grader,” according to Woodward. It also quoted the secretary as saying that defence chiefs “don’t always get to choose the president they work for.”

Mattis was one of the first top administration officials to deny the book’s claims.

"The contemptuous words about the President attributed to me in Woodward’s book were never uttered by me or in my presence,” Mattis said in a Sept. 4 statement. “While I generally enjoy reading fiction, this is a uniquely Washington brand of literature, and his anonymous sources do not lend credibility.”

But Trump’s most direct public criticism of Mattis followed the book’s revelations.

“I think he’s sort of a Democrat, if you want to know the truth,” Trump said in an interview on “60 Minutes” in October. “He may leave. I mean, at some point, everybody leaves. Everybody. People leave. That’s Washington.”

He walked that back a bit in November, telling reporters who asked if would remove Mattis after the midterm election, “no.”

Mattis was a defence secretary of few words in public. Asked in a May 2017 interview on CBS News about what keeps him up at night, Mattis responded “Nothing. I keep other people awake.”

But he occasionally let slip an intemperate remark during his military career. In 2005 during a speech in San Diego, Mattis was quoted as saying it was “fun to shoot some people,” that “it’s a lot of fun to fight,” and “it’s a hell of a hoot.”

Even before he took charge of the Pentagon, Mattis and Trump were in sync in their views on Iran. Mattis called the Iran nuclear deal reached under President Barack Obama “an arms control agreement that fell short” and labelled the regime in Tehran “the single most enduring threat to stability and peace in the Middle East.”

Mattis wasn’t always in lockstep with Trump. Like other foreign policy officials in the Trump administration, he spoke out against Russia’s meddling in the 2016 campaign and its actions in Syria and Ukraine. The National Defense Strategy published during Mattis’s tenure sought to focus US strategy toward “great power” relations with Russia and China, putting less emphasis on the fight against terrorism that came to dominate US thinking after the Sept 11, 2001 attacks.

In an administration infamous for leaks and turmoil, Mattis’s reticence to create controversy generated extra scrutiny the few times he appeared to subtly criticize the political climate in the U.S.

In August 2017, video surfaced of Mattis telling troops in Jordan that the US “has problems that we don’t have in the military. Just hold the line until our country gets back to understanding and respecting each other.”

Trump credited the blunt-talking Mattis with getting him to rethink his campaign pledge to revive waterboarding, an interrogation tactic used against suspected terrorists that Obama had banned. “He said, ‘I’ve always found, give me a pack of cigarettes and a couple of beers and I’ll do better,”’ the president-elect recounted to the New York Times.

Mattis retired from the military in 2013 after a 41-year career in the Marines that took him from rifleman to head of US Central Command.

A native of Pullman, Washington, Mattis had more than 30 years’ experience in the Middle East, where he first deployed in 1979 as an infantry company commander. Later he led the North Atlantic Treaty Organization’s transformation office and rewrote -- along with Army General David Petraeus -- the military’s counterinsurgency field manual. He was one of few military officers who identified US economic debt as a national security issue.