Reproductive rights have taken center stage in Democratic campaigns.
Control of the Senate could hinge on the outcome of the race, which has seen six months of bruising attack ads and remains deadlocked in public polls.
The debate was the second of three scheduled for this week, making it an important stretch in a pivotal campaign.
Similar measures calling for labeling genetically modified foods have failed in recent years in California and Washington, and Vermont is being sued for the labeling law it enacted earlier this year.
The nonprofit group founded by Karl Rove is spending $9.7 million in an effort to defeat incumbent Democratic Sen. Mark Udall.
In a tight race for U.S. Senate, incumbent Mark Udall faces Cory Gardner. The outcome could determine whether Republicans gain control of the Senate.
Incumbent Republican Mike Coffman and Democratic challenger Andrew Romanoff are locked in a tight race for Colorado's 6th Congressional District.
Locked in a tight race, Democratic Gov. John Hickenlooper and his Republican challenger, former U.S. Rep. Bob Beauprez, showed their political spark at a debate Tuesday.
The St. Louis-based agriculture giant joins Pepsico and Kraft Foods in donating to the No on 105 committee.