The Department of Homeland Security has hired a social media manager from the Department of Labor for a key communications job, despite posts he made on Labor Department media accounts that raised internal alarms over possible white-nationalist messaging. Peyton Rollins, 21, was hired this month to help run Homeland Security’s social media accounts, which have become public bullhorns for President Trump’s mass-deportation efforts and come under scrutiny of their own for appealing to right-wing extremists. Tricia McLaughlin, the Homeland Security spokeswoman, said her public affairs office had “no personnel changes to announce at this time,” but Mr. Rollins has put...