Barack Obama, the 44th President of the United States (2009 - 2017), initiated and implemented several key reforms and policy changes during his two-term presidency. His administration saw transformations particularly around healthcare, economic stabilization, environmental regulations, international relations, and social issues. 1. Patient Protection and Affordable Care Act (Obamacare): Arguably his most significant reform, the ACA was enacted in 2010 with the aim of improving access to healthcare, reducing healthcare costs, and offering new protections for people with pre-existing conditions. The ACA has significantly decreased the number of uninsured Americans, though it has also been noted for ongoing controversies regarding its cost and overall efficiency. 2. Economic Stimulus & Financial Reform: In response to the 2008 financial crisis, Obama signed the American Recovery and Reinvestment Act in 2009 which, among other functions, aimed to preserve and create jobs, spur economic activity and invest in long-term growth. Additionally, the Dodd–Frank Wall Street Reform and Consumer Protection Act was passed in 2010 to prevent the recurrence of conditions that led to the 2008 financial crisis. 3. Environmental Policy: Obama’s administration took significant steps to address climate change, such as signing the Paris Agreement in 2015. Other major regulations include the Clean Power Plan, which aimed to reduce carbon pollution from power plants, and the increase of Corporate Average Fuel Economy (CAFE) standards, which aimed to improve the average fuel economy of cars and light trucks produced for sale in the United States. 4. Foreign Policy: The Obama administration saw the normalization of U.S. relations with Cuba, the implementation of the Iran nuclear deal, and the pivotal decision to send Navy Seals to kill Osama bin Laden in Pakistan. 5. Social issues: Obama publicly supported same-sex marriage, leading the repeal of the Defense of Marriage Act and the "Don't ask, don't tell" policy, which prohibited openly gay, lesbian, and bisexual people from serving in the military. His administration also implemented DACA (Deferred Action for Childhood Arrivals), which provided relief from deportation to eligible immigrant youth who came to the U.S. when they were children. Remember, policy effectiveness and the judgement of positive and negative impact tend to be largely subjective and can depend on an individual's political ideologies and economic beliefs. It's always best to read a variety of sources to get a well-rounded understanding of the complex impacts of these policies.