Spending by independent groups had little election impact, analysis finds

Spending by outside groups, it turns out, was the dog that barked but did not bite. Obama and other Democrats had long made dire predictions about the potential impact of the Supreme Court’s 2010 decision in Citizens United v. Federal Election Commission, which allowed corporations and unions to spend unlimited money on elections and created a new class of wealthy political groups.
…
If either Romney or Obama had held a substantial cash advantage, it is possible that one candidate could have dominated in the final weeks of the campaign. But the two camps were roughly evenly matched by the end. The result was a kind of dreary equilibrium, as both sides clogged the airwaves with so many attack ads that Republicans began airing spots in California and other deep-blue states.