The Trump administration has announced what it is calling “a major step forward” in the fight against a class of toxic chemicals called PFAS , or per- and polyfluoroalkyl substances. Extended exposure to PFAS, often referred to as “forever chemicals” because they can persist indefinitely in the environment, has been linked to various cancers, autoimmune diseases, and other harms. On Monday, Secretary of Health and Human Services Robert F. Kennedy Jr. lauded Donald Trump as the first president who is “completely committed” to removing forever chemicals, which are found at unsafe levels in tap water in some 80 percent of congressional districts and lurk in the blood of 97 percent of Americans .  But what Kennedy considers a step forward looks like a big step back to most of those who have long kept an eye on the issue.…