AP decided it was necessary to “fact check” something that Donald Trump said, that was true, but they claimed it was false anyway. In their explanation they said:
THE FACTS: Only partially true. Syria’s President Bashar Assad considers the Islamic State group to be among numerous “terrorist” groups that threaten his government. His overstretched military is mainly focused on combating Syrian opposition groups, some of which are supported by the United States. Assad does use air power against IS-held areas and his ground forces are engaged in fighting with the extremists in Deir el-Zour in the east.
Just because Donald Trump does not list every group that Syria is fighting ever time he names any single one of those groups, does not mean he is wrong. It is fair to say that fact checking from the media is unreliable and untrustworthy.