I'm not sure if I agree, that will take some time to consider.
However, a source for this "Later when asked about the Overton window, Lehman admitted that the purpose of the Overton window was to convince potential donors of the role of think tanks in public policy." seems necessary.
>Shifts in the Overton window do not come about simply with the suggestion of radical policy proposals
If those proposes are frequent enough, and adopted widely, they do.
>Change only comes in the face of a tidal wave of evidence and an energized advocacy strategy.
People could not care less about "evidence" (unless it supports their side), and an "energized advocacy strategy" is another way to describe what the author tried to deny, the "overton window shifting" by advocacy.
The only myth here, is that it doesn't have to happen by radical advocacy (to get people to "meet in the middle"). It can just as well happen by very slowly gradually moving towards one or the other direction regarding some topic. So, you could just add tons of +0.1 proposals and get to move to +10 eventually, you don't need to propose +50 in the hopes you'll get to +10.
However, a source for this "Later when asked about the Overton window, Lehman admitted that the purpose of the Overton window was to convince potential donors of the role of think tanks in public policy." seems necessary.