No one living in the United States can be denied healthcare regardless of their insurance status, citizenship or anything else. I have worked as a healthcare worker since 1972 and have never, ever seen anyone turned away. For one thing, it is completely illegal to do so, especially for any hospital, Urgent Care or Emergency Room that is tax exempt, inspected by any government agency such as CMS, JCAHO, NRC, FDA, EPA or any other health related services agency of the U.S. government and the 50 State governments. The only facilities that can deny healthcare to someone for lack of insurance are those indicated as Self Pay facilities that do not receive any kind of government funds and most of those few and far between facilities are generally specialty facilities.
Not only can nearly 98% of all healthcare facilities not turn folk away, they also can not demand payment if the person is unable to do so. And, none of this reflects on the kind of standard-of-care that patient receives. Those actually giving the healthcare have no idea of the patient's insurance or monetary status. We treat all patients the same from the President to the person who is homeless living on the streets.
So, in a sense, the U.S. already has universal healthcare. The only question that is currently being asked then is how will it be paid for? As currently is with those who do have insurance (mostly the middle and upper income populace & businesses that provide employer plans to their staff) paying for it with ever increasing insurance premium costs to make up for the many who do not have it, or the U.S. Government by raising the taxes of the middle and upper income populace & businesses that provide employer plans to their staff. Six one-half dozen of the other. The only difference is, with U.S. Government calling the shots there will be a steady increase of interference from Washington lawmakers deciding what is appropriate healthcare instead of the insurance companies doing it as they are now. Either way, bureaucrats (government or private industry) are making the rules and the middle and upper income folks still pay for it.