This is why we have the second amendment. And the constitution as the thing to which office-holders swear allegiance to rather than to "the party" or "the president".
There are plenty of examples of the US army (Vietnam, Iraq, Afghanistan), and US controled dictators forces (Cuba) being beaten or stalemated by guerilla forces. Depending on how widespread and committed a revolution was, they could have a very good chance imo. Also if the revolution is extremely popular, then elements of the army will side with them.