As government agencies, academic centers, and researchers affiliated with them provide an increasing share of the science base for policy decisions, they are also subject to efforts to politicize or silence objective scientific research. Such actions increasingly use sophisticated and complex strategies that put evidence-based policy making at risk. To assure the appropriate use of scientific evidence and the protection of the scientists who provide it, institutions and individuals must grow more vigilant against these tactics. Maintaining the capacity for evidence-based policy requires differentiating between honest scientific challenge and evident vested interest and responding accordingly, building and diversifying partnerships, assuring the transparency of funding sources, agreeing on rules for publication, and distinguishing the point where science ends and policy begins.