As lawmakers consider repeal-and-replace, they will need to tackle a major conundrum: how to make health insurance more affordable while tending to the needs of very sick patients who may incur high costs. Tracy L. Johnson, Holly A. Batal, and Patricia Gabow examine the case of Denver Health, a health system that has built on the ACA’s Medicaid expansion and investments in health care delivery innovation to improve care and lower costs for high-need, high-cost patients.