In the first six months of 2018, 28.5 million Americans were uninsured — 20.1 million fewer than 2010, the year the Affordable Care Act was signed into law by then-President Barack Obama, according to data from the federal Centers for Disease Control and Prevention.

Among U.S. adults aged 18–64, about seven in 10 were covered by private health insurance plans in the first six months of 2018. Of this total, four percent or just under eight million people were covered by private health insurance plans obtained through the Health Insurance Marketplace or state-based exchanges.

The distribution of coverage, however, is uneven, as shown in the data for states that expanded Medicaid coverage compared to those that did not.

In the first six months of 2018, adults aged 18–64 in states that expanded Medicaid coverage for low-income residents were more likely to be insured than those residing in non-expansion states. For states that expanded coverage the uninsured rate was 9.1 percent compared to 18.1 percent in the states that did not.

In the 2018 mid-term elections, Idaho, Nebraska and Utah voted to pass Medicaid expansions, joining 33 states that had previously done so. In Montana, voters rejected a measure that would have introduced new taxes to continue funding a 2016 Medicaid expansion that is set to expire in 2019—leaving its status in limbo.