If you want, say, money to go to disease eradication in Africa, voting in the US doesn’t help much for that, but donating to private charity does.
That’s just the calculation here, and they are directly comparable. U.S. aid agencies also dispense the same interventions that the charities GiveWell and GWWC endorses do. If one can increase aid spending on those (as opposed to ‘aid’ for political purposes in Afghanistan, or to subsidize U.S. farmers) sufficiently to make up for increased government overhead/leakage they’re very directly comparable. U.S. Congress members and presidential candidates vary quite a lot in their stances on foreign aid, and helping those keener on effective aid in tight races can be compared reasonably directly against StopTB Partnership or the like.
That’s just the calculation here, and they are directly comparable. U.S. aid agencies also dispense the same interventions that the charities GiveWell and GWWC endorses do. If one can increase aid spending on those (as opposed to ‘aid’ for political purposes in Afghanistan, or to subsidize U.S. farmers) sufficiently to make up for increased government overhead/leakage they’re very directly comparable. U.S. Congress members and presidential candidates vary quite a lot in their stances on foreign aid, and helping those keener on effective aid in tight races can be compared reasonably directly against StopTB Partnership or the like.