From C-SPAN (February 2, 2011): Witnesses testified about the constitutionality of the 2010 health care law. The hearing took place two days after U.S. District Court judge Roger Vinson ruled the law was unconstitutional. It was the fourth federal district court to rule on the constitutionality of the law, with two courts upholding the law, and two courts finding parts or all of it unconstitutional. (Click the link to view the entire hearing, 2hrs 44 mins)
Now consider this: If the Affordable Care Act were to be declared unconstitutional because of the mandate, wouldn't Social Security and Medicare also be struck down because of the mandated taxes by the federal government? Do you see where the Republicans are going with this?