Originally posted by: LordSegan
Declaring a "state of emergency" means nothing in the United States (it is regulalrly done such as during the California wildfires in October).
Here in the U.S., there is no emergency procedure to unilaterally suspend/change the Constitution or disband the Congress. If a president tried to do either, he would be committing treason, and I would be the first person in line to try to blow his head off with a sniper rifle.
To answer your question, if the entire Congress were killed, I imagine the president (or new president) would have the power to temporarily issue executive orders that would carry the weight of law.
If you are asking, "what would it take to get troops in U.S. cities".... again, that happens regularly, when state Governors order state National Guard units into cities.
It is illegal under the Posse Comitatus Act to use Federal troops in the U.S. unless there is an invasion or an actual insurrection.
http://en.wikipedia.org/wiki/Posse_Comitatus_Act
http://en.wikipedia.org/wiki/Insurrection_Act
Unlike Pakistan, we have laws for everything, and we usually follow them.