The president has declared an emergency for parts of Tennessee, Mississippi and Kentucky because of flooding.
The White House says the order signed on Wednesday means the Federal Emergency Management Agency and other departments can help the states coordinate all disaster relief efforts in parts of all three states.
Over the past two weeks, heavy rains and tornadoes have hit many areas, causing rising waters, infrastructure damage and dangerous roads.
In Tennessee, the declaration covers Dyer, Lake, Shelby, and Stewart counties.
In Mississippi, the counties of Adams, Bolivar, Claiborne, Coahoma, DeSoto, Issaquena, Jefferson, Tunica, Warren, Washington, and Wilkinson are covered. Several Kentucky counties are eligible and most are along or near the Ohio River.