Article snippet: 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. ‘‘They have to get dramatically better and they have to get better quickly.’’ He said the idea is to work with the Mexican government ‘‘to make sure that things did get better.’’ Trump claims Mexico has taken advantage of the United States for decades but that the abuse will end when he slaps tariffs on Mexican imports next week in a dispute over illegal immigration. Trump tweeted Sunday: ‘‘America has had enough.’’ The president said last week that he will impose a 5% tariff on Mexican goods on June 10 to pressure the government of Andres Manuel Lopez Obrador to block Central American migrants from crossing the border into the U.S. Trump said the import tax will increase by 5% every month through October, topping out at 25%. But the president has been here before, issuing high-stakes threats over his frustration with the flow of migrants only to later back off. They include his threat earlier this year to se... Link to the full article to read more