The Overton Window is a tool used to visualize policy positions along the political spectrum. It was invented by Joseph P. Overton, a Mackinac Center for Public Policy scholar and Vice President, in the mid-1990's and has "gained national currency" since 2003.  In the Center's own description, it is designed to provide a spectrum which visualizes policies acceptable to the public with the various ends of the spectrum representing 'unthinkable' policies and the middle representing a policy that would be widely well received by the public. Any policy which would be deemed acceptable or desirable by the public is "in the window". The concept also holds that legislators can only act within the window out of their duty to constituents. According to the Center, the window is also finite and can be moved. The Center advocates action by think tanks and other non-political figures which would "shift the window", bringing policies that would once be thought of as radical or unthinkable into the realm of possibility, allowing legislators to enact them. Consequently, policies once looked upon acceptable or desirable would move out of favor with the public.