The Trump administration aggressively publicized the arrests of more than 8,000 immigrants by federal agents since Inauguration Day, with the promise that those detained would be part of a historic mass deportation. But NBC News has learned that some have already been released back into the United States on a monitoring program, according to five sources familiar with the operations.Since he took office, President Donald Trump and his allies have promoted immigration operations in cities like Chicago and New York, where agents across federal agencies were called in to increase the number of arrests.But arresting more people inside the United...