Outside spending has been increasing over the past several cycles (and was doing so even before Citizens United.) Open Secrets reports:
According to a Center for Responsive Politics analysis of the latest super PAC filings (disclosed earlier this week with the Federal Election Commission), conservative super PACs have spent $137.1 million through the end of July. That's more than four times the amount that their liberal counterparts, which have managed to spend just $31.1 million through the same period.
Breaking down super PAC spending on a month-by-month basis, it's clear that the conservative groups had a major jump on the liberal ones -- in large part because of spending fueled in the closely contested Republican primary -- but in recent months, liberal super PACs have stepped up their spending. For instance, liberal super PACs spent more in the month of July than they did the entirety of 2011 and the first four months of 2012 combined -- about $8.3 million compared to $6.1 million. Meanwhile, in June, the partisan gap narrowed to its closest point -- liberal super PACs spent $9.5 million, while conservative groups spent $11.3 million.
But just as liberal groups appeared to be catching up, the conservative super PACs stepped on the gas. In fact, the very next month, in July, conservative groups spent a total of $27 million, which nearly matched the total that liberal super PAC groups have mustered this full election cycle so far.