The Bern is purest on the concept of Medicare for All - there will be no role for private insurance in his plan as he states it.

Others have used the phrase "Medicare for All" really to refer to a public option. Private insurance can still be used, instead of something like Medicare, but something like Medicare is available for those who want it or have no private options.

According to the link, Warren is playing politics, using the phrase "Medicare for All" to win over the Bern set, but not being clear about whether she really means single payer as in: that's the only payer, like in Bern's plan, or more like "it's there for those who want it".

She certainly stood with Bern in the debates and did not choose to highlight the possibility of retaining the private option when she was challenged last week. In fact she didn't even challenge the idea that taxes would go up for everyone - she indicated that "working families", whatever that means, will see costs drop overall, so not to worry about that increased tax bill.

As maybe the likeliest winner of the nomination at this point, I hope she is leaving herself wiggle room to go more for a public option than pure single payer.