The Koch brothers and their network of wealthy conservative donors recently announced that they intend to spend almost $900 million on the 2016 elections. This level of spending by a group operating independently of any candidate or political party would be unprecedented in American politics. In fact, it would exceed the combined spending by the Democratic National Committee and the Republican National Committee during the 2012 election cycle. Understandably, this announcement reinforced concerns among Democrats and liberals that spending by the Koch brothers and other conservative groups could give Republican candidates a crucial advantage in key House and Senate contests and in the race for the White House.
Since the Supreme Court’s 2010 Citizens United decision opened the door to spending by Super PACs funded by unlimited contributions from corporations, unions, and wealthy individuals, there has been a dramatic surge in spending by outside groups on federal elections. In 2012, according to data compiled by the Center for Responsive Politics, groups not affiliated with any candidate or party spent over $1 billion on the presidential and congressional elections, more than three times the amount that such groups spent in the previous presidential election year. In 2014, outside groups spent over $565 million, almost twice the amount that such groups spent in the previous midterm election year.
Conservative groups spent more than $250 million in support of Republican Senate candidates in 2014, including almost $35 million in North Carolina, more than $33 million in Colorado, and more than $31 million in Iowa. Republican candidates won all three of those races and almost every other key Senate contest, scoring a net gain of nine seats in the upper chamber.
https://www.centerforpolitics.org/crystalball/articles/why-outside-spending-is-overrated-lessons-from-the-2014-senate-elections/