His success should have two consequences: others should emulate his methods; and those who this time bet against his forecasts on the basis of wishful thinking will be unlikely to repeat their error.
This means that it will be harder to make money by betting on the next election, as markets will be pricing in more scientific method and less flim-flam.
How, then, will a Nate Silver wannabee make money with such poor odds? He can only do so by betting with borrowed money - in effect leveraging up to improve his returns.
But this carries two dangers. One is exposure to tail risk, as even the best methods occasionally go wrong: as Nate said, 8% chances do come up once in a while.
The other is performativity risk. If voters believe that a particular candidate is likely to win, they might not turn out. Because the leading candidate - by definition - is the one who attracts widespread but lukewarm support, he might be more vulnerable to this, which would put the election result back into doubt.
What I'm describing here is no mere possibility. It's a pretty close analogy to what happened with mortgage derivatives; people geared up, thinking they were onto a safe way of making money but in fact were magnifying risk rather than reducing it.
This is an example of what Andrew Lo calls adaptive markets. A smart guy (Nate Silver) sees a way of making money, but as people emulate him, profit opportunities turn into losses. Just as there are population cycles in biology, so there are profit cycles in finance: the waxing, waning and waxing again of returns on small cap stocks since the 1980s is just one example of this.
And it's not just in financial markets that this is true. Billy Beane and his hero Arsene Wenger (pbuh and a painful death to his enemies) have seen their success dwindle as lesser men emulated them (though perhaps this also shows that big money beats brains).
The message here is that intelligence, science and ability might make you money - but perhaps only briefly, and trying to repeat your tricks can lead to losses.