It was said up thread there should be riots if the Senate caves on whomever Obama nominates. That would be the perfect excuse for him to declare martial law. Just the treat of martial law would be enough for the Senate to cave. It will be a vicious circle with any number of starting points but the end point is all the same.
Who will enforce Martial Law? There are not enough Police,National Guard, or Military Forces to enforce Martial Law in this country. In a smaller country, county,city, or town yes. This country would be much harder.