Senators Sheldon Whitehouse (D-RI) and John Barrasso (R-WY) introduced the ACO Assignment Improvement Act. The legislation would expand Medicare Accountable Care Organizations (ACOs) to include nurse practitioners, physician assistants, and clinical nurse specialists. “No matter where you live, you ought to be able to go to a health care provider,” said Kilmer. In Rhode Island, ACOs care for roughly 41,000 patients.