I don't know Sander's plan or the details. BUT if it works like Medicare, as I know it, then a premium is paid to the government and out of that premium are paid the benefits. 80/20. After that the person has the ability to buy supplemental plans or advantage plans, which the insurance companies are falling over themselves to sell to those on Medicare.
So I can see that working. I am not sure how you are not saying Medicare is not single payer now.
One major problem is, I think there is vast rip off of Medicare going on today. That would need fixed, if possible.
That's more than most people know.
Medicare Supplements are completely free market-based. So they cover the gaps left over by deductibles and the 80/20 co-insurance. Plus, standard Medicare has no annual out-of-pocket maximums, so people who only have Medicare can still get nailed. The "F" Medicare Supplement, for example, pays pretty much all bills for Medicare-approved treatments. You then need a standalone PDP, Prescription Drug Plan, to go with it. So, for the whole package, a 65-year old will pay around $200-$250 per month.
With Medicare Advantage plans, the government pays a private insurance company per member per month (PMPM) to take over your Medicare. Then those companies can compete to offer the lowest premiums and provide the most extra goodies, like (extremely helpful) health club memberships. They include the drug plan. Because of the PMPM arrangement with the government, these premiums are much lower (even $0), but the plans have small co-pays like regular PPO & HMO plans.
I specifically separate Medicare from "single payer", because true single payer allows for no free market competition.
Here's the thing: About 80% of our health care costs go to people already on Medicare, 65+, for obvious reasons, they're much sicker. Putting young and healthy people on this would MASSIVELY shrink the average cost curve. Plus these individual plans would take a MASSIVE cost monkey off the backs of American employers.
It's sitting right there. It already works. We can make it more efficient with time. But our "leaders" are cowards.
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