"For U.S. EPA at the Supreme Court, it's been the best of times -- and the worst.
In Clean Air Act cases, EPA is on a roll. The high court last term upheld a major EPA program for air pollution that drifts across state lines. It also barely trimmed a permitting program for greenhouse gases, leaving intact most of EPA's first round of climate regulations.
And even when EPA has technically lost, as in the landmark 2007 Massachusetts v. EPA climate case, the justices ruled for the more environmentally protective side -- in that case, that EPA is empowered to regulate greenhouse gases."