In reality, I'm not sure I believe there's such a thing as a 95-98% probability of one major party winning in a country like the US. One can argue whether it's appropriate to fudge in additional uncertainty but there are a lot of things that could happen in the week before the election (including but not limited to candidates dying) that could throw existing poll results up in the air.

[ADDED: Or maybe something like that really is a few percent probability and you can end up with a 95% probability anyway. It just feels as if there's some upper limit to what you can measure using polls.]