This paper raises two questions central to lawmaking and policy implementation in the American separation-of-powers system. First, under what institutional conditions do we observe variation in bureaucratic compliance with legislative dictates in contemporary statutory implementation? And second, given inter-branch battles over policy implementation, how does the tool of statutory amendment enable Congress to rein in administrative capacity and move policy back toward its own preferences once bounds have been transgressed? I seek to answer these questions in the context of the Environmental Protection Agency. The study provides the first empirical analysis of the extent of, and the conditions underlying bureaucratic noncompliance in policy implementation in the US, providing support for the hypotheses that under conditions of divided government with large partisan majorities as well as amid partisan divisions in Congress, the EPA increasingly deviates from congressional preferences in implementing the delegating statutes. However, results examining the EPA's deviations from the statutory text present a puzzle that is deserving of further inquiry. The paper further provides preliminary evidence of considerable policy movement as a consequence of these ongoing inter-branch battles over environmental policy implementation in recent years.