i think what he means is if and when the constitution came under significant attack, they would then use the weapons to fight the government
obviously, this is flawed logic. for two reasons, firstly as has been pointed out, by swarm i believe - the constitution has already been altered/suspended in the past, post 9/11 for example. yes, this could be considered an emergency, but the likelihood is any future suspension would also be cloaked within a real or imagined or fabricated similar event. there are documents proving the u.s government has in the past considered and planned false flag attacks on it's own people/troops in order to provoke war, in that particular case with cuba
secondly, and more importantly. it would be near impossible to organise mass rebellion on a scale needed to topple the government. remember the riots over here... online channels were monitored to such an extent that the authorities knew exactly where, when and how many people these groups would contain. ringleaders were arrested extremely quickly
now imagine this in america, in a state of emergency. the government would know exactly what level of response was needed, where to go and would be legally entitled to shoot armed groups by the thousand. perhaps this wouldve been possible pre internet/mobile phone age - now, the government hold all the cards
as i mentioned before, a couple thousand people with assault rifles is a force to be reckoned with on a county/state level. youd probably give the police and even state home guard a run for their money. but as soon as the federal machine swung into action, that would be brushed aside with impunity. you can't fight tanks and air support with small arms fire. even grenades would be unlikely to trouble modern heavy battle tanks like the m1 abrams. it would be a massacre, followed by a ruthless, digital manhunt of those involved who managed to escape. but whatever gets you to sleep at night i guess