2. Obamacare Debate
During Obama's first term, the president pushed a then Democrat-controlled Congress to pass the Affordable Care Act. The measure succeeded in March of 2010 without a single Republican vote.
Since then, the ACA, commonly called Obamacare, has endured several legal challenges and a bill passed by a now GOP-controlled Congress calling for its repeal.
Considered Obama's signature legislation, its fate remains precarious in light of mixed results in its implementation and the in-coming Trump administration vowing to repeal it.