WASHINGTON (Reuters) - President Donald Trump kept up his criticism of Mexico on Friday, saying it “has taken advantage of the U.S. for long enough,” as a crisis over border security and trade deepened. “Massive trade deficits & little help on the very weak border must change NOW!” Trump wrote on Twitter.  On Thursday, Mexican President Enrique Pena Nieto scrapped a planned trip to Washington to meet Trump, who has repeatedly demanded that Mexico pay for a wall on the U.S. border to halt illegal immigration.      The White House also suggested on Thursday that the United States could impose a 20 percent tax on goods from Mexico to pay for the wall, sending the peso tumbling. Speaking about the scrapped summit, senior Trump aide Kellyanne Conway on Friday told Fox News that “the relationship was not imploded. This one meeting has been canceled and that was a mutual cancellation.” In a separate interview on CBS News, she said the tax was one funding possibility and waved off the chance of Mexican retaliation that could cost American jobs, telling CBS News: “They can do what they want.” “Mexico should pay for that wall because they get an awful lot from this country,” Conway told CBS. The White House has said its tax proposal is in the early stages.  A plan being weighed by House Republicans would exempt export revenues from taxation but impose a 20 percent tax on imported goods. The idea, known as a border adjustment tax, would be a significant change from current U.S. policy. Retailers and other businesses that sell imported goods are not keen on the idea, and some lawmakers have expressed concern about its impact on U.S. consumers.  “The costs for everything from groceries, to cars, to office supplies would go up by 20 (percent), making it harder for middle class families to pay for things they need every day,”     Senate Democratic Leader Chuck Schumer said in a statement.     