Colorado may be the No. 1 election battleground in the U.S. for Republicans, if the money pouring into the state is any measure.

Independent groups reported spending $9.4 million on federal campaigns there between Sept. 1 and Oct. 12, more than in any other state, with $7.5 million -- 80 percent -- going to help Republican candidates, records show. Leading the way were two groups advised by strategist Karl Rove, American Crossroads and Crossroads GPS, which said yesterday they have raised $56 million for races nationwide, exceeding their $50 million goal.

The state may provide the best measure of the power of outside money in American elections this year. Critics say a Supreme Court decision that freed corporations to spend funds from their treasuries on elections has spurred a flood of special interest money that’s mainly helping Republicans.