Election law scholar Rick Hasen offers a truly stunning visual representation of the impact of Citizens United on our elections:
As his chart shows, spending by outside groups seeking to change the result of the 2012 presidential election is just under $90 million — or more than double the amount of outside spending by this point in the 2008 election. This is true, moreover, despite the fact that the 2012 cycle still has nearly eight more months to go, and despite the fact that there is only one contested primary in 2012 while both Democrats and Republicans had a hard-fought primary battle in 2008. As a possible sign of just how far Citizens United may go in injecting big money into the race, outside spending in in congressional election years grew nearly nine times between 2006 and 2010.
Lest there be any doubt, it also appears very unlikely that spending benefiting Democrats will simply cancel out spending benefiting Republicans. Rather, as of January, seventeen of the top twenty donors this cycle were conservatives:
Update:
Professor Hasen emailed ThinkProgress and pointed out that this data measures total spending through March 8 in each election cycle, not through the entire election cycle. We have corrected that error and struck an erroneous part of one sentence.