An individual mandate at the state level is just as unconstitutional. If you can force people to buy a service at gunpoint, what’s to stop Michigan, for example, from forcing people at gunpoint to buy one of their Detroit cars?
It is not unconstitutional according to the constitution. It may be wrong.
The Founders left these powers to the states. If the state does wrong, the people of that state have a political way to easily correct it. If the people refuse to correct it, in theory you can move to a neighbor state that is not committing that wrong.
But even here, Newt gets very fuzzy when pressed in interviews about this mandate. It actually sounds like he would be satisfied if, bottom line, people who have used healthcare but left others holding the bag for it are held accountable.