Families wash clothing in a a river under a highway bridge in Coamo, Puerto Rico, a city on the southern coast of the island on Monday, October 2, 2017.
The warning comes as much of the island remains without access to drinking water in the wake of Hurricane Maria, which tore across Puerto Rico last month.
Ryan says "we've got to do more to help Puerto Rico rebuild its own economy" but that the immediate humanitarian crisis must be addressed.
"It is shameful that President Trump is threatening to abandon these Americans when they most need the federal government's help", said Maryland Rep. Steny Hoyer, the second-ranking House Democrat.
Trump's latest outburst immediately touched off criticism.
"There are reports of residents obtaining, or trying to obtain, drinking water from wells at hazardous waste "Superfund" sites in Puerto Rico", the agency said in a statement Wednesday. Some also noted that as the island was reeling from Hurricane Maria, the president was instead tweeting about NFL players' behavior during the national anthem.
Only 17 percent of the island has electricity, according to the site. There are now 18 sites in Puerto Rico on the National Priorities List.
"After Trump's most recent comments, Cruz responded via Twitter, "@POTUS It is not that you do not get it; you are incapable of fulfilling the moral imperative to help the people of PR. Shame on you!"
ABC- President Donald Trump said Thursday the federal government can not keep the Federal Emergency Management Agency (FEMA) in Puerto Rico "forever", even as the USA territory continues to reel from the devastation wrought by Hurricane Maria in September. It has killed at least 45 people, and about 85 percent of Puerto Rico residents still lack electricity.
The tweets Thursday morning are just the latest attacks the President has launched on the US territory, which was devastated by two hurricanes last month.