Even before President Donald Trump and Gov. Gavin Newsom squared off over Trump’s decision to send National Guard troops to quell immigration protests, before Newsom likened Trump to a dictator and Trump endorsed the idea of arresting the governor, the question of how much California could continue to rely on FEMA was front and center.

After catastrophic flooding in central Texas left the area devastated, the Trump administration’s lackluster response offers a chilling glimpse of what’s in store for when the next disaster strikes.

With the nation’s attention focused on the need for the federal government to effectively respond to disasters, White House officials are emphasizing instead their plans to overhaul the agency, sayin...