The number uninsured Americans was cut down by one-third according to a report released on Monday by the U.S. Department of Health and Human Services (HHS). Between 2012 and March 4, 2015 the percentage of Americans without insurance dropped from 20.3 to 13.2 -- a 7.1 percentage point drop or 35 percent reduction.

"That's quite simply an historic reduction in the uninsured," the Director of Health and Human Services' Office of Health Reform, Dr. Meena Seshamani, told reporters. It is the largest drop in the ranks of the uninsured since the expansion of Medicare and Medicaid, 50 years ago during the Johnson administration.

The Affordable Care Act (ACA) turns five on March 23 of this year, and since the its implementation in 2010, 16.4 million adults (excluding the elderly) gained health insurance. Overall, it is estimated that 5.7 million young adults between the ages of 19 and 25 gained insurance since 2010. Between 2010 and October of 2013, 2.3 million young adults ages 19-25 were insured due to a provision in the ACA allowing them to stay on their parents' insurance plan. After October of 2013 -- when the healthcare exchanges first opened -- an additional 3.4 million young adults acquired health insurance.

"The Affordable Care Act is working to drive down the number of uninsured and the uninsured rate," Richard Frank, HHS assistant secretary for planning and evaluation, stated at a press conference. "Nothing since the implementation of Medicare and Medicaid has seen this kind of change."

The change was seen across populations. The uninsured rate of Latinos dropped 12.3 percentage points (from a baseline of 41.8 percent uninsured). For African Americans the level dropped 9.2 percentage points, starting at a base of 22.4 uninsured, and for white Americans, the uninsured rate dropped 5.3 percentage points (with a starting base of 14.3 percent uninsured).

States with Medicaid expansion also saw a drop in the ranks of those without health insurance. "This was particularly true in expansion states where families with incomes of 138 percent of poverty or less had the lowest rates of health insurance coverage prior to the coverage expansion (55 percent were uninsured)," the report explains, "and the largest gain in coverage after expansion -- a 13 percentage point increase, nearly twice the percentage point increase that occurred in non-expansion states (7 percentage points)."

Despite the overall drop in uninsured populations, the report does have some gaps. It does not track how many children gained insurance, nor does it highlight populations that are still uninsured. The report also does not distinguish how individuals received insurance -- whether from ACA exchanges, an employer, Medicaid, or individual insurance outside of the ACA marketplace.

"I think it's important to recognize that we're in entirely new territory here," Frank said to reporters.

"We're just really starting to understand more completely who we've really brought in, and also who is left uncovered," he continued.

The Affordable Care Act is the cornerstone piece of legislation for the Obama Administration. However, Republicans object to Obamacare, and Republican lawmakers have attempted, and failed to repeal the ACA more than 50 times.

Despite lawmakers' lack of success in repealing ACA, the fate of Obamacare is still in uncertain terms. The legislation could be gutted by the Supreme Court. The case King v. Burwell, which was heard earlier this month, targets the federal subsidies provision of the law, which allows those who make less than four times the poverty level to receive subsidies to help pay monthly fees. Only 16 states set up their own healthcare exchanges (Covered California, for example). The other 34 states use Healthcare.gov run by the federal government. The case argues that the 34 states using the federal exchange are not eligible for subsidies. If the Supreme Court rules against the federal subsidies -- a key portion to making the ACA work -- many people in 34 states would not be able to afford healthcare.