Very little looking on your part Konor will document laws in the U.S. since the late 80's that anyone who stumbles into any ER must be "medically evaluated" and "anti-dumping" laws prohibit transfer to public hospitals of those without insurance; with very large monetary penalties and possible suspension from Medicare participation for doing so.
So the "undocumented", homeless, un-insured, and many of the Medicaid eligible use ERs at their site of primary care...creating many hour waits for everyone.
The quality of that care is certainly not the Mayo Clinic standards, unless the uninsured happens to live in North Scottsdale wink but the personal injury tort system in our country assures some kind of care for the uninsured.