Man, I didn't realize big sites were this complex under the hood. That site wasn't even complicated; if I recall correctly it was just some info pages and payment. I don't know anything about backend stuff. All my projects are like this: [traffic] -> [hosted server] -> [Amazon CloudFront files]
I believe this includes all of their internal tools for campaigning and organizing and suchlike, not just the public website.
You want a citizen to be able to receive emails and give you money, then move smoothly to calling other citizens through the website, being provided with a walk sheet to go door-to-door in her own neighborhood, eventually leading a small team of other volunteers.... all of these require interaction with the database of other supporters. Ideally the campaign has over a hundred million people all contacting each other and urging each other to vote a certain way.