Final answer:
The Affordable Care Act (Obamacare) significantly increased the number of Americans with health insurance, with approximately 20 million gaining coverage, reducing the uninsured rate from 16% in 2010 to around 8.6% by 2020.
Step-by-step explanation:
Since the Affordable Care Act was passed in 2010, many more people in the United States have health insurance than before. The ACA, also known as Obamacare, introduced mandates, subsidies, and provisions to reduce healthcare costs and expand insurance coverage.
In particular, it addressed issues of underinsurance by subsidizing insurance for low-income individuals and prohibiting denial of coverage due to preexisting conditions. This legislation led to a significant decrease in the uninsured rate, from 16% of the population in 2010 to around 8.6% by 2020, meaning that 20 million Americans gained coverage under the ACA.