WASHINGTON — The CIA has sent out an internal email cautioning employees against posting political messages on social media after a senior officer posted a pro-Palestinian image on Facebook. The email to staff members was “simply a reminder of existing policy,” a U.S. official told NBC News. The warning was issued after the agency’s associate deputy director for analysis posted an image depicting a man waving a Palestinian flag that is sometimes used in commentary critical of Israel. The Financial Times first reported on the social media post. The career analyst who posted the image has not been disciplined, a...