Rhetoric is style, not substance, and challengers don't pass legislation with their rhetoric. Elections are about winning votes, and the rhetoric you use during a campaign should be designed to do that. No purpose is served in losing votes due to rhetoric.
But passing legislation is completely different, because even if it costs you votes, you've managed to achieve something.
Look at Obama. He ran and won by mouthing vague platitudes so as not to offend anyone, and actually conned some Republicans into thinking he was just this moderate guy. But then when he got into office, he managed to pass a lot of substantive legislation and regulation that angered a lot of people.
The fact is that such a strategy works.