Quite a few Democratic candidates for office this year are campaigning on the idea of enrolling everyone in Medicare. It’s not just the left. A significant number of doctors in the American Medical Association are for it. Public opinion polls show that 70% of Americans like the idea.

Here are ten things you need to know.

1. 1. Medicare is not really government insurance.

Almost everybody on the political left thinks that Medicare is a government plan – one that is completely different from private insurance. Yet that view is wrong.

Although Medicare is largely funded with tax dollars, it has never been a strictly government program. Medicare’s original benefit package copied a standard Blue Cross plan that was common back in 1965. And Medicare has always been privately administered – in many places by Blue Cross itself. That’s the same Blue Cross that administers private insurance sold to non-seniors.

Moreover, in recent years, one-third of all seniors – and perhaps as many as half of young seniors – are enrolled in plans offered by Humana, Cigna, UnitedHealth care and other private insurers under the Medicare Advantage program. These private plans are virtually indistinguishable from the private insurance non-seniors have.