The American military can do many things. A coup is a quick action of taking the power away from a government. The military’s job is to make sure everyone is safe. If there is a problem or terroristic issue that is about to take place, the military may take action against the impending threat and danger. A civilian government could mean a few things. It could mean a separate government has been established that is technically not part of the country.
A revolt may ensue. This happened already in the 1800s with the Civil War. Usually, this happens in third world countries. Even though the military could plot a coup, it is unlikely that this will happen since there are major obstacles that would stand in its way.