WASHINGTON (Reuters) - U.S. President Donald Trump on Sunday backtracked on his push for a cyber security unit with Russia, tweeting that he did not think it could happen, only hours after promoting it following his talks with Russian President Vladimir Putin. “The fact that President Putin and I discussed a Cyber Security unit doesn’t mean I think it can happen. It can’t,”  Trump said on Twitter. He then noted that an agreement with Russia for a ceasefire in Syria “can & did” happen. 