Citizens United ruling has boosted Republicans in state races

Republican candidates have enjoyed a small but statistically significant advantage in winning state legislative races since the 2010 Citizens United Supreme Court decision, according a new study.

The case - in which the Supreme Court ruled that corporations have the same freedom of speech guarantees afforded under the First Amendment as individuals - resulted in billions of dollars in spending, especially from conservative groups. In turn, this yielded a six percentage-point increase for Republican candidates, the study found.

In five states (Colorado, Iowa, Texas, Wisconsin and Wyoming), Republican candidates were seven percentage points more likely to beat their Democratic rivals. In four states (Michigan, Minnesota, Montana and Ohio), that advantage increased by 10 percentage points or more. And in two states, North Carolina and Tennessee, the GOP candidates were 15 percentage points more likely to win.

The researchers focused on 22 states where Citizens United overturned bans on independent expenditures by corporations and labor unions, comparing them to 28 states where those bans never existed.

The study entitled "The Business of American Democracy: Citizens United, Independent Spending and Elections" was conducted by Tilman Klumpp of the University of Alberta, Hugo Mialon of Emory University and Michael Williams of Competition Economics.

"We document significant efforts, funded by corporations, to elect Republican candidates through independent expenditures in the 2010 state legislative elections in Colorado, Michigan, Minnesota, Montana, North Carolina, Ohio, Pennsylvania, Texas and Wisconsin," the authors wrote. "With the exception of Pennsylvania, there are all state in which Republican election probabilities increased significantly relative to their synthetic controls in 2010."

They added that they could not find a liberal independent expenditure initiative funded by unions that matched conservative efforts in 2010.