Scientific studies used by the Obama administration to help justify tough environmental regulations are coming under intensifying scrutiny, with critics questioning their merit as the Trump EPA reverses or delays some of those rules. In one case, agencies determined the research used to prop up a ban on a particular pesticide was questionable. On another front, the Environmental Protection Agency never complied with a congressional subpoena for the data used to justify most Obama administration air quality rules. “EPA regulations are based on secret data developed in the 1990s,” Steve Milloy, who served on President Trump’s EPA transition team, told...