WASHINGTON – A top official at the U.S. Department of Education has been keeping a controversial flag linked to Christian nationalism and the Jan. 6 insurrection hung outside his office, according to the agency's union and a department employee who has observed it. It's the latest in a series of instances in which the flag – which depicts a pine tree and the words "An Appeal to Heaven" – has been associated with agencies and figures at the highest levels of the federal government. Though long tied to the American Revolution, the banner in more recent years "has been adopted...