Legally, the difference is that the latter two programs are government operations, whereas the individual mandate would have compelled people to buy a private product. Helvering v. Davis (1937) was the famous (or infamous) case wherein the U.S. Supreme Court found that the Social Security Act was constitutional.
For a non-lawyer, the distinction is silly. The stated goals of all three programs — Medicaid, Medicare, and Obamacare — are to lay paving stones on the path to so-called “universal” coverage. The Founding Fathers had no notion of government-run health care, so they would surely find it absurd that 20th and 21st-century jurisprudence allowed that Congress can tax Jack to pay for Jill’s health insurance, and tax Jill to pay for Jack’s health insurance, but cannot tax Jack to pay for Jack’s (or Jill to pay for Jill’s) health insurance.
Read the entire article here.