The House and Senate still have to iron out six key differences between their versions of the legislation before Obamacare can be signed into law. But getting past the House and Senate may just be the beginning of the plan’s problems. Not only are the attorneys general of13 states jointly investigating whether Sen. Ben Nelson’s (D-NE) Cornhusker Kickback violates the Constitution, but multiple public interest law firms are promising to also challenge whether the scheme’s individual mandate meets constitutional muster.

Now conservative activists are adding yet another post-passage hurdle for Obamacare survive. The Denver Post reports:

Coloradans will likely be asked in November to blunt the impact of federal health-insurance reform with a state constitutional amendment that would attempt to undo some of what Congress is trying to pass.

Jon Caldara of the Independence Institute said Tuesday that he is still working on the language for his proposal, which would then need signatures from 76,047 voters to make the ballot. But he intends to find out in the fall whether voters want to stop the federal government from dictating insurance requirements to Coloradans.

At the same time, a freshman state lawmaker says she’ll push her legislative colleagues to opt the state out of the congressional health care reforms.

The state measures would be two of at least 14 similar plans being advanced by conservatives and libertarians across the country. Courts will likely have to decide whether states have the authority to trump or opt out of a federal mandate, but the proposals underscore how the health-insurance debate is already moving from Washington to state legislatures.