Earlier in the day, Reid had suggested that all of the horror stories being told about Obamacare -- including in ads sponsored by the Koch group Americans for Prosperty -- were "untrue."
He later clarified that it was only the "vast, vast majority" of those ads that were inaccurate.
The Koch organization noted that one of its ads features a woman suffering from leukemia who shares her story, and it accused Reid of attacking someone with cancer.
The Koch brothers have emerged as popular bogeymen for Democrats in recent months.
(Video above clipped by the Washington Free Beacon)