Mexico has hardened its opposition to President Donald Trump by saying it would retaliate if the United States imposed a border tax and that it can afford to lose financial aid that might be pulled to pay for a border wall. Foreign Minister Luis Videgaray said Mexico could respond to any tax the US were to unilaterally impose on imports from its southern neighbour to finance the wall with levies on select goods, aimed at US regions most dependent on exports south of the border.