regarding your first paragraph, look at the WWII Warsaw ghettos where small groups of armed Jews held off the Nazis for some time. If EVERY adult American was armed and willing to fight the government, do you REALLY think the army would win?
Really?
There are (approx) 1,400,000 active duty soldiers, and the same in the reserves right now, compared to about 109,000,000 U.S. citizens *fit for military service* age 18-49 in the United States .(link <link>
No, if the whole (or a large part) of the populace was armed AND willing to fight and die for their cause, they could very well overthrow their government. Many citizens are ex-soldiers as well, you know. How would the army be able to do anything with the entire country against them? How would they even EAT?
Even urban riots can be hard to put down until they die out on their own, so if The People REALLY wanted to overthrow their government,
They Could.