On February 10, Syrian President Bashar al-Assad, while welcoming a notion that U.S. troops might fight alongside Syria, rejected the proposal for safe zones as "not a realistic idea at all". Turkey unveiled a new proposal for safe zones to Sunni Arab states meeting February 13 in Bahrain. On 19 December 2018, President Trump announced that he ordered the pullout of all 2,000-2,500 U.S. troops operating in Syria, though no clear timetable was given. U.S. operations in al-Tanf continued into 2019. On 29 March 2017, during the Presidency of Donald Trump the United States Secretary of State Rex Tillerson expressed that the longer term status of president Bashar al-Assad is to be "decided by the Syrian people". This appears as a policy shift, since under president Barack Obama’s administration, the US made the departure of Assad a key policy aim. On March 30, 2017, United States Ambassador to the United Nations Nikki Haley reaffirmed that the priority of the United States policy concerning Bashar al-Assad is to no longer force him out of power. On 7 April 2017 US missiles destroyed Shayrat Air Base in Homs Governorate which US military claimed to be the base for the aircraft that carried out the Khan Shaykhun chemical attack three days earlier. In April 2018, The US, The U.K. and France carried out missile strikes against Assad's compounds in response to the Douma chemical attack. On 17 June 2020, reports claimed that the US imposed tough new economic sanctions under the Caesar Act, targeting anyone doing business with the Syrian President Bashar al-Assad from anywhere in the world. The sanctions were imposed to compel the Syrian government to halt its human rights abuses on civilians and accept a peaceful political transition. For the first time, the US has targeted Bashar al-Assad's wife, Asma al-Assad, claiming that she is "one of Syria's most notorious war profiteers".