WASHINGTON — For generations, official American documents have been meticulously preserved and protected — from the era of quills and parchment to boxes of paper to the cloud, safeguarding snapshots of the government and the nation for posterity. Now, the Trump administration has sought to expand the executive branch’s power to shield from public view key administration initiatives. Officials have used apps like Signal that can auto-delete messages containing sensitive information rather than retaining them for record-keeping. And they have shaken up the National Archives leadership. To historians and archivists, it points to the possibility that President Trump will leave...