President Trump has reversed a White House–approved rejection of federal disaster aid for California to help the state with the costs of its historic wildfire season. The reason for the initial rejection remains unclear — prompting speculation that the move may have been an attempt by Trump to follow through on his repeated threats to withhold wildfire aid from the state.

On Wednesday, the Trump administration denied California governor Gavin Newsom’s September 28 request for a major disaster declaration for six wildfires that struck the state that month, including the...