Migrants who pass through Mexico en route to the US will no longer be able to seek asylum in the United States, the Trump administration announced on Monday. The policy, which comes into effect on Tuesday, states that those arriving at the southern US border will not be allowed to apply for asylum if they have passed through another country first. It is designed to halt the large flows of migrants arriving from Guatemala, Honduras and El Salvador, but will also impact Cubans, Haitians, citizens of African countries, and others. The plan will certainly be challenged in the courts. William Barr, the attorney general, said that the United States is "a generous country, but is being completely overwhelmed" by the burdens associated with apprehending and processing hundreds of thousands of migrants at the southern border. "This rule will decrease forum-shopping by economic migrants and those who seek to exploit our asylum system to obtain entry to the United States," he said. Central American asylum seekers turn themselves in to US Border Patrol after illegally crossing the Rio Grande in Los Ebanos, on June 28 The number of migrants seeking asylum has dramatically increased in recent years. In 2009, there were 35,811 asylum claims, and 8,384 were granted. During the 2018 budget year, there were 162,060 claims filed, and 13,168 were granted. In January the Trump administration announced a “remain in Mexico” plan, by which asylum seekers would remain on the Mexican side of the border while their claims were considered. There is currently a backlog of 800,000 asylum cases, meaning many applicants wait many years for their plea to be heard. The “remain in Mexico” plan is currently being challenged in the courts, but is operational at the moment, despite the controversy. Mr Trump may find that his own tweets thwart his plans, given that he has frequently described Mexico as crime-ridden and highly dangerous. On Sunday evening Guatemala's Constitutional Court blocked President Jimmy Morales from immediately declaring the poor Central American nation a “safe third country” for asylum-seekers, amid growing pushback to US pressure that it absorb large numbers of migrants. "The rule, if upheld, would effectively eliminate asylum for those at the southern border," said Lee Gelernt, of the American Civil Liberties Union (ACLU). "It is patently unlawful."