Original sentence: Colin Mortimer, the Director of the Center for New Liberalism at the Progressive Policy Institute, has claimed that in the 21st century, the "Overton window" concept has been altered from its original form by political extremists, who have misinterpreted it as a strategy rather than a theorem
Edited sentence: In the 21st century, the "Overton window" concept has been altered from its original form by political extremists, who have misinterpreted it as a strategy rather than a theorem