First of all, they are arrogant know it alls, secondly they know Obama has the martial law card, thirdly they know the Repubs have done nothing. A well used 2nd Amendment is all they would fear.
There would be no case in which a national martial law would be reasonably imposed, short of a real invasion by a foreign army (not likely). Governors would declare martial law not the president. Trying to play that card (whatever you think that means) would probably not play out as you might imagine.