All of the methods by which a dark horse can run and win are there. The state will not remove your votes or intimidate voters not to vote for you. You will not be poisoned by radioactive toxins to prevent you from running. You will not be kidnapped, or your family threatened, or a bomb set off in polling locations. This isn't in any way like so many other actually repressive regimes. All you have to do is go and run.
We have more power in this society than anyone in any other. So why do we claim we're powerless? Because it makes us feel better that we're so lazy. I could run for office, but that might restrict my time watching The Office. Better to just say that running is pointless, so I don't have to make the change I want to see.
And even if you don't want to run, you can vote for independents, you can complain to your representatives, you can organize your friends and neighbors to petition local government for local reforms and participate in larger state and federal efforts. Individually we may be a drop in the bucket, but collectively we are a wave. You can't say that isn't powerful.