But I will opine that if we can't undertake such a venture simply because it is hard, that will be a sorry commentary on the state of our nation.

If we don't do it, it won't be because it is hard. It will be because it will make too many people worse off than they are now.

Measures that make a discrete group of people materially worse off in order to confer a smaller benefit on a much larger group of people don't fare well in our political system. Again, people that lose something they already have usually resent it more than people value gaining something they don't have. And the group of people who are facing a largish loss are far more likely to organize around preventing it than even the larger group of people who would have the modest gain. The people who are going to lose out care a lot, while the people who would gain care only a little.

To pass single-payer health care, whether all at once or in increments, you need to keep the number of people who are net-losers under the changes small - and hopefully politically weak. Unfortunately, that's probably not possible.