"Democratic senators are taking millions of dollars from insurance and health-care interests and getting lobbied by those donors and coming out against a position that 76 percent of Americans agree on," said Adam Green, interim chief executive of Change Congress.

"Will Mary Landrieu sell out Louisiana for $1.6 million?" says one Internet ad that suggests a link between contributions she has received from the medical industry and her reluctance to back the creation of a government-sponsored insurance option.