Trump's attitude towards Syria and Assad has changed very much.

Obama was widely criticized for his inaction in the Syrian civil war. His failure to act on the “red line” ultimatum he declared against Syrian President Bashar al-Assad’s use of chemical weapons remains one of the most scarring events in his administration. In April, Trump was quick to react with a one-off strike of his own after the Syrian government killed scores of civilians in an apparent chemical attack. But the attack was mostly seen as a show of force rather than part of a broad strategy in the war-torn country. 

Pentagon officials have emphasized they will keep the United States out of the conflict and have pushed back against a proposal, favored by some White House officials, to prevent Assad and his Iranian allies from moving toward parts of southern Syria occupied by the Islamic State. But the White House agreed in early July to cooperate with Russia in backing a civil war cease-fire in the southwestern corner of the country.