And if Russia or China was participating to a significant degree in our internal politics, that would come out as a national security issue and should be dealt with in other ways.
I know that my position isn't popular, but the Federalist papers talked about this issue, and took the position that for every David Koch there is a Tom Steyer. Why not let them waste all of their money fighting each other? There are several recent examples illustrating that money doesn't buy elections. Maybe it's not a fact yet, but there's enough evidence behind it that I think it's a defensible position.
If this takes off, I think the end result will be less participation in the political process by average Americans, who fear retaliation down the road. Maybe it looks like a difficult balance to you, but I think I would always come down on the side of more speech rather than less.