Not if the election wasn't won with a majority.

Sure it is, if there's a 30%/70% split of viewpoints then the 30% viewpoint is a mainstream viewpoint as well, not some weird niche - it's also considered normal and conventional (though less popular than the 70% one), shared by a significant part of the people, known / acknowledged by almost everyone including the opponents.

Sure it is. No one claims driving a Honda Accord isn’t a mainstream choice just because they aren’t the number one selling car.