...is there a difference? The donors tend to have just as much of an agenda to push
It might also be the case that one single "donor" puts in like 60% of the budget.
But that is also no different from one single client being 60% of your revenue.
In both cases, they'll be calling some shots.
I think the point is that the donors should have an another political agenda than the political agenda of whatever companies that pays for ads.