President Trump said last week that he would cut off aid to Guatemala, Honduras and El Salvador, the home countries of most of the migrants arriving at the United States’ southern border to seek asylum.

The Trump administration has already taken the first step to act on the president’s directive, notifying Congress that it wanted to divert the $450 million allocated to the region. By Monday, though, the administration had not offered details about whether any aid — such as military aid or support to combat drug trafficking — might be exempt from the order.

If the aid withdrawal does go ahead, aid advocates say, it would probably affect the region’s most vulnerable people, including small farmers struggling to adapt to climate change and teenagers pressured to join gangs in a region that is a major drug transit route, according to State Department estimates. Advocates say that, should these threats to lives and livelihoods grow, many more people will take their chances on the road and leave for the United States.

The decision to end aid is likely to provoke anger in Congress, where lawmakers in both parties have supported efforts to address the root causes of migration. If the money is ultimately withheld, it would affect a wide range of programs designed to improve citizen security, promote economic development and encourage accountable government.