No way would the dictator win. The US military relies on a huge amount of logistics. Fighting happening on US soil would severely undermine that. You can't exactly bomb your own cities with B-52s, because that's where the bombs are made. The US military would draw maybe a few million people - the rest of the populace would still be over 300 million people with a gun for every single person. Furthermore, it's virtually impossible for the military not to split under a dictator that fights their own people.