Yes. It was passed by the congress (our legislative branch), signed by the President (our exectutive branch), and has not been struck down by the courts (the judicial branch). If you are correct, then it would be simple to challenge it and have it overturned. Or if the people don't agree, then congress can overturn it.
Let me sum up:
the legislative branch thinks it's constitutional
the executive branch thinks it's constitutional
the judicial branch thinks it's constitutional
the people of the united states think it's constitutional
It's constitutional...