The focus must be life and safety." Trump signed a disaster proclamation for Texas on Friday night.
The disaster unfolding in Houston appeared suddenly, starting with severe storms Saturday evening that came with slashing, sideways rain and almost uninterrupted lightning.
Brays Bayou, a huge waterway crossing the southwestern part of the city, rose between 10 and 20 feet overnight and by Sunday morning was flowing over bridges in its path.
The Texas National Guard has deployed across the state, including engineers in Corpus Christi and an infantry search-and-rescue team in Rockport.
By morning, a city that had been largely spared by Harvey's initial pounding of coastal communities was flooded to devastating levels. Central time, the National Weather Service had recorded close to 25 inches of rain around Houston.