Are health insurance mandates constitutional? They are certainly unprecedented. The federal government does not ordinarily require Americans to purchase particular goods or services from private parties.
The closest we come is when government imposes a condition on the grant of discretionary benefit or permit. For instance, in most states, you must have auto insurance to drive a car, or you are required to install fire sprinklers when building a new house. But in such cases, the "mandate" is discretionary you don't have to drive a car or build a house. Nor do you have a constitutional right to do so.
But Americans do have a constitutional right to live in the United States. Accordingly, neither federal nor state governments can require you to purchase health insurance as a "condition" for residency.