they are saying that it is constitutional because they think it
needs to be constitutional, not because the law remains (or the actions of congress in passing this law) within the bounds set forth in the constitution. and that is the living document theory at work. "the constitution means what I damn well want it to mean".
"This ruling is well out of the mainstream of judicial opinion," Stephanie Cutter, an assistant to President Obama, wrote on the White House's blog after Judge Roger Vinson in Florida ruled that the entire law is unconstitutional. "Today’s ruling ... is a plain case of judicial overreaching. The judge’s decision contradicts decades of Supreme Court precedent that support the considered judgment of the democratically elected branches of government that the Act’s 'individual responsibility' provision is necessary to prevent billions of dollars of cost-shifting every year by individuals without insurance who cannot pay for the health care they obtain."