Final answer:
Obama's most significant health care effort was implementing the Affordable Care Act, offering accessible and affordable health insurance, which succeeded unlike Clinton's previous attempt. The correct option is 3.
Step-by-step explanation:
The most important health care effort of President Obama's presidency was implementing the Affordable Care Act (ACA), commonly known as Obamacare. The ACA represented a significant overhaul of the American healthcare system with the goal of providing accessible and affordable health insurance to all Americans, mandating insurance coverage, and reducing healthcare costs.
Although President Clinton also aimed to reform healthcare, his initiative failed to pass through Congress. Unlike Clinton's proposal, Obama's health care reform was successful, despite being met with considerable opposition and controversy, which led to some significant reforms being dropped before the act was passed.