US President Donald Trump on Sunday named Patrick Shanahan as acting secretary of defense to succeed James Mattis and said the pullout of US troops from Syria, which caused the Pentagon upheaval, will be “slow and coordinated”, in recognition perhaps of the criticism he has faced since.After a phone conversation with Turkey’s President Tayyip Erdogan, Trump said Sunday morning in a tweet, that, “we discussed ISIS, our mutual involvement in Syria, & the slow & highly coordinated pullout of U.S. troops from the area”. But, he added, “they are coming home”.President Trump announced earlier in the week, also after a phone call with President Erdogan, that the US will be pulling out its 2,000 troops stationed in Syria to fight the Islamic State (which is also called ISIS — Islamic State of Iraq and Syria). No timelines had been offered since.But the stunning decision, which was opposed by most of the president’s senior aides and advisers and was not discussed with allies, was greeted by a storm of criticism at home and abroad.Secretary Mattis, who had opposed the decision, resigned in protest after failing to persuade the president to change his mind. He should get himself some one who was more “aligned” with his own thinking, he told the president in a resignation letter that has received widespread attention, and irritated Trump.So much that he wants him out sooner than February till when Mattis had offered to stay to enable the president to look for a successor. Trump announced on Twitter that Shanahan, who is currently serving as deputy secretary of defense, will take charge from January 1. “Patrick has a long list of accomplishments while serving as Deputy, & previously Boeing. He will be great!”Before moving to the Pentagon, Shanahan had served as senior vice president for supply chain and operations at Boeing, starting at the company in 1986, according to his biography on the US department of defense website. His assignments there included a stint as vice president and general manager of the 787 Dreamliner, leading the programme during a critical period.Shanahan holds a Bachelor of Science degree in mechanical engineering from the University of Washington, and two advanced degrees from the Massachusetts Institute of Technology: a Master of Science degree in mechanical engineering, and an MBA from MIT’s Sloan School of Management.Mattis, his predecessor, was a celebrated US marine general.Shanahan is now the third senior member of the Trump administration charged with an “acting” assignment, following — acting chief of staff of White House Mick Mulvaney and acting attorney general Matt Whittaker (Trump has named William Barr to assume full-time charge when confirmed by the senate)..