A major economic crash may well lead to sporadic violence, if not anarchy. But martial law would still be almost impossible to impose on a national basis, short of an absolute catastrophe (multiple simultaneous nuclear detonations, i.e. - TEOTWAWKI). Short of such a horror, it would be almost impossible for the Federal government to persuade state legislatures to cancel the elections in the fall. The Alinsky model does apply however, in using Progressive organizations to militate for increased government power and control over people and property.
Tanks in the street and boots on the ground would not be needed to effect martial law. Except for the 10 percenters,the population could be goaded into quick submission by control of the food, energy, and communication supply chains. Grocery store's would be empty within 24 hours. Few would be able to survive and resist by their own skills and resources.