Anis Amri, 24, who had spent time in prison in Italy, was stopped by two officers during a routine police check Friday morning.
Twelve people were killed and 48 others hurt when a truck plowed into a popular Berlin market Monday. The Islamic State has claimed responsibility.
Two German newspapers reported the truck ran into the market outside the landmark Kaiser Wilhelm Memorial Church on Monday evening.
Obama has a self-interest in tutoring Trump, who pledged to wipe out key Obama legacy items as soon as he gets into office.