In the week that President Trump took on social media, Axios has learned that he had a call Friday with Facebook CEO Mark Zuckerberg that was described by both sides as productive.Why it matters: With the White House and Twitter at war, Facebook has managed to keep diplomatic relations with the world's most powerful social-media devotee.Zuckerberg wrote in a Facebook post on Friday: "I've been struggling with how to respond to the President's tweets and posts all day. Personally, I have a visceral negative reaction to this kind of divisive and inflammatory rhetoric. ... But I'm responsible for reacting not just in my personal capacity but as the leader of an institution committed to free expression." "I disagree strongly with how the President spoke about this, but I believe people should be able to see this for themselves, because ultimately accountability for those in positions of power can only happen when their speech is scrutinized out in the open."