Ben Gilbert describes himself on Bluesky, the social media app, as an “economist, lit and guitar nerd, rugby fan, owner of excessive pets.” A professor at the Colorado School of Mines, he rarely posts, but when he does, the subjects reflect his expertise in natural resources. So it was odd when a video purporting to be a news report appeared on his account last month, blaming France’s financial and political support for Ukraine for police staff shortages at home. Without his knowledge, Mr.