Make no mistake: Although the United States may well be headed for a catastrophic economic crisis, we are already in a monumental political and constitutional crisis. As a historical matter, were the House Republicans to push the country into the abyss, they would be creating a situation analogous in the past only to the nullification crisis of 1832 and the secession crisis of 1860-1. The emergency is that grave.

So what should President Obama do? First, he must make the self-evident case that if the Republicans go through with their threat to take the country over the fiscal cliff, they will have violated the 14th Amendment of the Constitution that states: “The validity of the public debt of the United States, authorized by law, including debts incurred for payment of pensions and bounties for services in suppressing insurrection or rebellion, shall not be questioned.” Explaining that the Republicans propose to act unconstitutionally would immensely strengthen his position in this emergency no matter what. He needs to make the argument loudly and clearly, without the lawyerly diffidence he has displayed.

The burden in this crisis rests entirely with the congressional Republicans who have precipitated it. If they were to violate the Constitution, it would be their fault, not the president’s. The president needs to make that argument as well – crisply and loudly....