From Einav and Finkelstein (2023):

…whereas 12.5% of people below 65 are uninsured at a cut-off date, twice as many—one in 4—are uninsured in some unspecified time in the future over a 2-y interval. Furthermore, the chance of dropping insurance coverage remained nearly unchanged with the introduction of the landmark ACA. Danger of insurance coverage loss is especially excessive for these with medical health insurance by Medicaid or non-public exchanges; they’ve a 20% likelihood of dropping protection in some unspecified time in the future over a 2-y interval, in comparison with 8.5% for these with employer-provided protection.  Those that lose insurance coverage can expertise extended intervals with out protection; about half are nonetheless uninsured 6 mo later, and virtually one-quarter are uninsured for the following 2 y.

Regardless of the passage of ACA, dependable medical health insurance within the US is actually solely out there to the aged, veterans and people with steady jobs.