Who provides shelter to a million people converging on a city?
Do you know what winters in the US are like? How do you keep those people warm enough to continue protesting in 10° (-12°C) weather? You can't just say "people will have to figure that out for themselves", people will literally freeze to death if you do that.
A cold winter was instrumental in defeating the Nazis in Russia, wasn't it? Everyday civilians are not trained soldiers, are not accustomed to spending long periods in freezing cold, and for the most part don't own the proper equipment that would even make such a thing possible.
Are you going to equip them? Feed them?
These things don't just come together overnight or without a huge amount of planning and logistics. The fact that you think it's as easy as "driving to the capitol and staying there" just goes to show how little you've actually thought about this.
Edit - just for context, there are roughly 115,000 hotel rooms in the DC Metro Area. Even with illegal double occupancy, that's 800,000 people living on the streets, underequipped, in winter.