Obama is not mandating anything. In fact his "proposal" needs a two thirds majority in the senate to pass..
Nothing in the constitution allows the president to mandate anything. He may issue executive orders. An example is when George H Bush gave an executive order forbidding assassination. Any sitting president can change an executive order with one of his own.
The tenth amendment has never really been tested in the court. It is still considered an ambiguous amendment because there is so much disagreement about it between states and the federal government.
I believe that Bush's election by the supreme court violated states rights. The Supremes overruled the Florida Courts who had ruled in Gore's favor.
The Enumerated Powers Act.. is a proposed law that would require all bills introduced in the U.S. Congress to include a statement setting forth the specific constitutional authority under which the law is being enacted. In every Congress since the 104th Congress, U.S. Congressman John Shadegg has introduced the Enumerated Powers Act, although it has not been passed into law. At the beginning of the 105th Congress, the House of Representatives incorporated the substantive requirement of the Enumerated Powers Act into the House rules
Now this wasn't done according to house rules...why because it's unconstitutional. Pelosi couldn't even site the article in which this would fall to a CNS news reported when asked.
When lawsuits are presented if or when this bill is passes, this bill will be defeated because of the lack on constitutionality. Now if this bill passes muster with SCOTUS, then you will witness a revolt in one form or another.