Mulvaney said if the three Central American countries do not curb migration to the USA, "there's little reason to continue sending them money".
President Donald Trump has escalated his persecution of immigrants and refugees, ordering the cutoff of all U.S. aid to the Central American countries of Honduras, Guatemala and El Salvador because the right-wing US-backed regimes in all three countries (which comprise the so-called Northern Triangle of Central America) have been unable to halt the flow of desperate refugees moving north toward the United States.
On Saturday, Secretary of State Mike Pompeo announced that, at the president's direction, the State Department was ending its foreign assistance programs for the three Central American countries for 2017 and 2018.
Experts fear that cutting aid programmes will exacerbate problems in the three countries and force more people to migrate.
On Sunday, government officials defended the polemic decision by claiming that it is a way to ask those nations "to do more" to prevent migrants from going to the United States, and that they needed "to send a message" to those territories.
The state department said it would "engage Congress in the process", suggesting that lawmakers would need to approve the cuts.
"Closing off the border makes no sense at all, '" the Maryland Democrat said Monday on CNN's "Newsroom".
The Trump administration says it is struggling to deal with a surge of asylum seekers from Central America who travel through Mexico.
Salvadoran Treasury Minister Nelson Fuentes said US aid in his country includes $20 million in technical and fiscal funding over five years, and the government has not gotten word of any cuts.
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"That program would be severely curtailed without the USA funding", Ray said.
The U.S. President's political campaign against immigration could take new and more risky dimensions.
Congressional aides and USA officials said they were trying to establish what money would be eliminated, and even some of Trump's fellow Republicans questioned the wisdom of curbing the aid, much of which aims to reduce violence, gang activity and the illicit drug trade - all factors that send migrants north.
As Politico newspaper reported on Friday, about $627 million that Congress allocated for Central America one year ago had been long in limbo at the White House Office of Management and Budget.
"I don't think they thought it through", he said. The funding does not go to the governments of El Salvador, Guatemala or Nicaragua.
The administration is hoping policies of deterrence will reduce the number of people who turn themselves in to USA border agents, overwhelming the capacity of processing centers along the southern border.
Over the last decade, Manny Galvez, a volunteer at the Catholic Worker House in Iowa City, has helped dozens of people fleeing their home countries in Central America settle in places like Iowa.