But politics is not about policy. Political donors want to signal their affiliation with their tribes, not spend their money efficiently to change the world. It's a modern potlatch. Otherwise they'd be giving to something else in the first place - it's extraordinarily unlikely that giving to the Democrats or Republicans is the maximal way to impact the world, so anyone who is doing it obviously doesn't have the goal of efficient charity.

I predict that such an organization would capture < 0.5% of donors by # and < 0.1% by $. That's a pretty small market - a few hundred thousand.