Here is what USA Today writes:
Think tanks and public policy non-profits – researchers of policy papers, creators of panels and advocates for causes ranging from a balanced budget, to lower taxes to a stronger military – share the same 501c3 charitable designation in the tax code as charities that provide social services.
Gifts to foundations could be the first casualties if the charitable deduction is lowered to 28% from 35% for individuals making more than $200,000 or couples making more than $250,000, as suggested by the White House. Other plans, including those from former Republican presidential nominee Mitt Romney, would cap overall deductions for top earners from $17,000 to $50,000.
Because think tanks and public policy groups rely so heavily on donor contributions instead of government grants, they would be affected "disproportionately" by any change in deductions, said Diana Aviv, president and CEO of Independent Sector, a leadership network for America's non-profits.
It's unlikely donations would stop, but they would probably be reduced as wealthy donors look for the best way to give, said Melissa Berman, president and CEO of Rockefeller Philanthropy Advisors.