Deputy Secretary of Defence Patrick Shanahan, a former Boeing executive with no military experience, will take over for Mattis on January 1.
In a letter to all branches of the United States armed services, Mattis pens, "Our Department's leadership, civilian and military, remains in the best possible hands". So keep the faith in our country and hold fast, alongside our allies, aligned against our foes.
"I appreciate the opportunity afforded to me by this administration to serve alongside Secretary Mattis, our Service members and all the civilians who support them", White, who reported directly to Mattis, tweeted in the afternoon.
"You have the right to have a Secretary of Defense whose views are better aligned with yours on these and other subjects", Mattis wrote at the time, adding he would stay on until the end of February 2019 to allow time for a successor to be found and so that he could represent the U.S.at a NATO Defense Ministerial meeting.
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This had brought huge benefits to both nations' people and contributed greatly to world peace, stability and prosperity, Xi said. The US imposed tariffs on a number of Chinese products, including consumer and industrial items such as handbags and rice.
Sick plane passengers may have used airport water fountains
Once the plane landed in Tampa , all sick passengers deplaned and were checked by medical staff before officially being released. Tiffany McKinney, a passenger on the flight told WFLA-TV that people were "just coming out of nowhere" and throwing up.
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The impasse over Trump's border wall resulted in a partial government shutdown that entered its ninth day on Sunday. Trump wrote the deaths were "strictly the fault of the Democrats" for not agreeing to fund his wall on the U.S.
Acting U.S. Defense Secretary Pat Shanahan said Tuesday the department "remains focused on safeguarding our nation", as he officially took over the post left by the resignation of Jim Mattis.
Pentagon spokeswoman Dana White said Monday she would be stepping down from her position in U.S. President Donald Trump's administration after just over a year and a half in the role.
Mattis quoted from a letter Lincoln wrote in 1865 to Gen. Ulysses S. Grant. "The call is also a courtesy, and a mark of respect for the incoming Secretary of Defense". Mattis' replacement is a former defense contractor with no military experience.
While Shanahan has not always had day-to-day involvement in thorny geopolitical issues like this, Pentagon officials say he is ready to tackle them. His views on strategic issues such as US alliances and the wars in Afghanistan and Syria are largely unknown to the public. John McCain of Arizona for equivocating on whether he favoured providing defensive weaponry to Ukraine in response to Russian military intervention.
Little known outside business and Washington circles, Shanahan will be thrust onto the world stage at a time of tumultuous changes and unpredictable foreign policy moves under Trump.
A Washington state native, the 56-year-old Shanahan spent more than three decades at Boeing, where he became senior vice president, worked on missile defense systems and was general manager of the 787 Dreamliner program.