Would a single-payer system be less constitutionally problematic than a mandate?

[True Federalist (진정한 연방 주의자)]

Depends on what you mean by single-payer.  If doctors were forced to be part of the single-payer system, then no it would be of doubtful constitutional validity.  But Medicare doesn't operate that way, and an all ages Medicare would likely withstand constitutional scrutiny unless we got a bunch of strict constructionists on the court who would also strike down pretty much the entire welfare state.