Congress has reached a deal on a spending bill that would require the military to stop using firefighting foam containing toxic chemicals linked to cancer, but would abandon efforts to place stronger regulations on the chemicals. The bill, called the National Defense Authorization Act, has been the focus of intense negotiations for months. House Democrats saw it as their best chance to force President Trump’s Environmental Protection Agency to increase its oversight of a class of chemicals, called perfluoroalkyl and polyfluoroalkyl substances — commonly known as PFAS — that have contaminated drinking water sources across the country.