Perhaps I am mistaken, but, would not one directly effect the other? If Wall Street ran a ten trillion dollar advertising campaign for me, wouldn't my popularity soar. And inversely, if Wall Street ran a ten trillion dollar advertising campaign AGAINST my opponent, wouldn't my popularity soar.
Yeah, sure. My point is that when we're measuring how much money is given to the candidates directly --- to their official campaign funds --- we are measuring donations from ordinary people, not from corporations. Therefore this sum of money will correlate with the popularity of the candidates without necessarily causing it.