Donald Trump has threatened to cut off millions of dollars of aid to Honduras if it fails to stop a group of as many as 2,000 migrants fleeing violence and poverty who are attempting to the reach the US border overland. Guatemalan police detained the migrant caravan’s spokesman on Tuesday, a day after the group defied warnings from local authorities and crossed the border from Honduras.

The Trump administration is considering taking back more than $3 billion in foreign aid that Congress already approved, in a move that senators from both parties are calling questionably legal and promising to resist.The Office of Management and Budget instructed the State Department and the U.S. Agency for International Development earlier this month to provide a balance sheet of foreign aid projects that have not yet been funded. Unless Congress intervenes, the money may be returned to the U.S. Treasury at the end of fiscal year on Sept. 30.