NHS is the UK's national healthcare. It is one of many national healthcare systems that exists in every major nation except ours.

Medicare is a government health insurance program. It pays much less than private insurance companies. If it was expanded to cover all Americans, there would be higher taxes but no need for Americans to buy private health insurance.

This would also stop skyrocketing medical costs, which is the one thing that could really threaten America's long term economy. Medicare pays less than private insurance because of its economy of scale. Were it the only single payer, it could dictate prices (within reason) because it would be a monopsony, which has the same market control power as a monopoly.