WASHINGTON — A top White House official said Sunday that President Donald Trump is ‘‘deadly serious’’ about slapping tariffs on imports from Mexico but acknowledged there are no concrete benchmarks being set to assess whether the U.S. ally was stemming the flow of migrants enough to satisfy the administration.
‘‘We intentionally left the declaration sort of ad hoc,’’ Mick Mulvaney, the acting White House chief of staff, said on ‘‘Fox News Sunday.’’
‘‘So, there’s no specific target, there’s no specific percent, but things have to get better,’’ Mulvaney said.