If I care about the election more than other charities, I won’t give to such a fund. My dollars will do more towards the campaign on average if I give directly to my side. This effect is trivial if the double impact group is small but very large if it is most donations.
In an extreme case, suppose that most people give to double impact and the two campaigns are tied $1b - $1b. One donor gives their $1m directly to their side. It is the only money actually spent on advertising; that side has a large advantage in ratio of funds spent.
More realistic scenarios yield smaller average ratios, but always less expected return for your preferred campaign if you give to it vs, double impact.
This doesn’t work as advertised.
If I care about the election more than other charities, I won’t give to such a fund. My dollars will do more towards the campaign on average if I give directly to my side. This effect is trivial if the double impact group is small but very large if it is most donations.
In an extreme case, suppose that most people give to double impact and the two campaigns are tied $1b - $1b. One donor gives their $1m directly to their side. It is the only money actually spent on advertising; that side has a large advantage in ratio of funds spent.
More realistic scenarios yield smaller average ratios, but always less expected return for your preferred campaign if you give to it vs, double impact.