Hey I don't have a dog in this fight, but I think this is the link you're looking for.

https://github.com/fivethirtyeight/checking-our-work-data

Here is the historical data for the 2018 House forecast:

- Web: https://projects.fivethirtyeight.com/2018-midterm-election-f...

- JSON: https://projects.fivethirtyeight.com/2018-midterm-election-f...

You are correct they do not publish the exact math of the forecasts, but you can see how the forecast changed over time.

The link I provided does actually show every single forecast 538 has ever made. OP was wrong when they said it was the raw data they use to make the predictions. Check out the link I provided, it has everything OP was asking for.

Nice! I didn’t poke into it much further cause I knew about this one.

Please look at the actual data on the linked page. Each of the csv files on that page has thousands of predictions 538 made going back as far as 2008. This isn't the raw data they used to make the predictions, these are the actual predications that they made.

Edit: For example, here are the headers on the file named presidential_elections.csv

year,office,state,district,election_date,forecast_date,forecast_type,party,candidate,projected_voteshare,actual_voteshare,probwin,probwin_outcome

These are the actual forecasts they made for presidential elections going all the way back to 2008.