Martial law is the suspension of civil authority and the imposition of military authority. General it occurs under times of civil strife, military invasion or political upheavel. Although there is no explicit mention in the Constitution, the suspension of Habeus Corpus can be accomplished directly by Congress or indirectly by the President as Commander-In-Chief.
The real question is could this ever happen here?
I believe it could be tried, but in the long run, it can't succeed.
The short answer as to why it wouldn't succeed is not some high moral or political reason but simply that this country is too big and complex to control by a single individual or small group. Even if the entire military were somehow willing to enforce what is essentially against their oath, there are insufficient forces to control even a small portion of the citizenry.
Another complicating factor would be keeping the economy from completely collapsing during such a transition. For example, one common act for a dictator or junta is to control the press and media to keep information from flowing to potential attackers. The internet, although it could be disrupted easily enough by compromising the root DNS servers and killing the backbone networks, the internet today is the basis of much of our economy, including the flow of finance, healthcare and general business operations. Without the internet being available many common services such as ATMs, checks, banking, and shipping simply stop working. The end result would be chaos, although it might seem like a good idea from a controlling perspective, the end result would be destroying all the value that might be had from ruling a rich country.
Further difficulties would come from outside the US, since we are still at the center of the world's commerce, and depend on both investment, markets and especially the import of oil. Without support from the world's economies (which would be expected in a coup of this type) the entire country would grind to a halt.
You can also imagine with this country being geographically spread out and with an insufficient force to manage it, cities or even states might splinter off and form pockets of independence. The end result would more likely resemble the breakup of Yugoslavia than a stereotypical "banana republic". Populations would like begin to move from areas under control to these splinter "countries" since the breakdown of commerce would mean many people would be without food and need to move to areas with supplies.
Clearly the larger cities might remain under the control of martial law since they are easier to control; but again with the difficulty of finding food it is likely that the populations would fight to leave.
How likely would the military support this act? Given that currently most of our military is overseas (especially in Afghanistan and Iraq) there are barely enough remaining to control one or two cities. It would be likely that the troops overseas would abandon their posts to return to the US to help their families, and depending on the circumstances they find would be more likely to support the populace that the government.
I imagine the only way this could work is if it was made to look like an attack but I have a hard time thinking it could be accomplished so well that enough people would be fooled. Despite continuing belief in 9/11 conspiracies, the fact is most governments leak like a sieve, and all it takes is for one person to leak this for it to be stopped. It makes a great movie plot, but in reality large conspiracies simply don't work.
Will we ever see full martial law in this country? I don't think so. It has happened before, under limited circumstances (Lincoln during the Civil War is the best example, but even there the Supreme Court said no) but I think anyone having a desire to turn the US into their personal plaything is likely to never get beyond the dreaming state.
Let's sure hope I'm right.
