According to the most recent Kaiser Health Tracking Poll,

83% of Americans support allowing Medicare to negotiate the price of prescription drugs (93% of Democrats and 74% of Republicans).

Source: "Searching for Savings in Medicare Drug Price Negotiations," The Henry J. Kaiser Family Foundation, February 9, 2016, http://kff.org/medicare/issue-brief/searching-for-savings-in-medicare-drug-price-negotiations/