Exactly. The bottom line is that Congress has a responsibility to only pass laws they deem constitutional. The President may only sign bills he believes are constitutional.
As a last defense, the courts will intervene.
Congress and the President made this a law with a wink and a nod, fully understanding that the bill was unconstitutional. They knew what the right thing was, and made a conscious decision to do nothing and throw the mess into SCOTUS' lap.
If both branches of congress, the president and the courts believe the bill is constitutional under our current form og government, isn't that the definition of consitutional ?