The Sunlight Foundation released a report on March 31 highlighting the 10 "big-money" races in the Senate. As Politico reported:
Campaigns, super PACs and other outside group have spent $11.5 million so far in the Ohio Senate race, more than in any other state, according to a new Sunlight Foundation reports. Maryland ranked second, with $8.8 million spent, and Illinois took third, with $8.5 million spent. Not surprisingly, all three races have had early, contested primaries. Ohio and Illinois held theirs on March 15, and the closely fought Maryland primary is April 26.