The U.S. Senate battle between reelected Democratic incumbent Sen. Michael Bennet and his Republican challenger Ken Buck won the title for the most expensive race with more than $33 million spent in favor of both candidates, with a slight majority favoring the GOP candidate with 54 percent of overall independent expenditures:
Race–Colo. Sen. Michael F Bennet, D (incumbent)
Last week–$5,964,300
Two weeks ago–$7,566,269
Three weeks ago–$4,878,765
Total–$33,435,827
Partisanship–54% Republican