"'American Crossroads, the super PAC founded by Karl Rove, spent $104 million in the general election, but none of its candidates won. The United States Chamber of Commerce spent $24 million backing Republicans in 15 Senate races; only two of them won. Sheldon Adelson, the casino mogul, spent $53 million on nine Republican candidates, eight of whom lost.' It was, as the paper noted, 'A Landslide Loss for Big Money.'"[1]
"When a candidate doubled their spending, holding everything else constant, they only got an extra one percent of the popular vote. It’s the same if you cut your spending in half, you only lose one percent of the popular vote. So we’re talking about really large swings in campaign spending with almost trivial changes in the vote."[2]
[1] - http://reason.com/archives/2014/07/14/dear-liberals-stop-fre...
[2] - http://freakonomics.com/2012/01/12/does-money-really-buy-ele...