Given that the US military boasts enormous firepower, what use is even widespread private gun ownership against such might?
Well, guns are a deterrent to tyranny. If a man actually uses a weapon against a government functionary, then the deterrent has failed, and the result is unfortunate.
The state will practice repression and double down on it again and again, but only for a time.
Its strength lies in its design as the monopoly punisher which can overwhelm any individual or private organization within its domain.
For example, the government may wipe out a whole city, murdering all men, women, and children in it, to strike terror into the hearts of others who might contemplate a rebellion.
But its crucial weakness is its tendency to make martyrs of those who resist it justly. The state cannot afford to slaughter "its own" people with tanks and attack helicopters... too much, for fear of turning public opinion decisively against it.
If that happens, the state's own soldiers will desert, refuse to protect the chiefs, and join the opposition.
There are never any guarantees, but on occasion, individual resistance can break the state's will to rule. The soldiers will drop their weapons; the prison guards will abandon their posts; the IRS agents will no longer evoke fear in the populace and disappear.
As a result, despite its massive military, the government's options are not unlimited.