It makes no sense for 1 dem and 1 repub to win. Thats not possible unless someone fucks up with the cheating.
Not my opinion, but this pundit disagrees with you, Lokmeer:
He thinks it'll be a split ticket, with a Republican and Democrat elected to the US senate.
But I see your point.
It's not a Presidential Election where there where multiple candidates or possibilities where a person decides to vote Trump or Biden, then chooses the other party instead of voting solidly Democrat or Republican.
It's just 2 cndidates from either party on one ballot.
There aren't all these 3rd party candidates this time round.
And a lot of those people who voted green, Libertarian whatever, might decide not to vote in this election and throw their support behind a Democrat or a Republican.
So that's the sleeper - the non-participants.
Overwhelmingly, it'll just be the voters who supported the Democrats or Republicans in the 2020 election and new voters thrown inta the mix who will bother to go out and vote while the 3rd party voters stay home.