I'll add to this.Right, but you're approaching this purely as a question of who to vote for.
"Swing voters" are a fictitious demographic in US politics. They no longer exist, least of all as capable of influencing election outcome. What replaced it are voters with partisan affiliation, whose decision point is whether or not to vote in the first place. 2020 was no different as it was a turnout battle, like every federal election since 2006.
The only faction in US politics right now with vested interest in preserving the myth of "the undecided 8%" are neoconservatives whose chickens came home to roost with Trump's ascent to power, and in the wake of it looking to influence the Democratic party further rightward rather than clean up their own mess.
The strategic goal of negative campaigning isn't to mobilize voters out of anger or fear. At least, not any more. It's now to demobilize voters who might cast a ballot for an opponent.
As far as positive messaging, here's where Democrats and Republicans differ. Trump is a credible source for "positive" messaging, at least in terms of how the majority of Republican voters see the world. Policy-wise, he's the same cloud of apartisan, imperialist, neoliberal miasma every president or presidential candidate has been since Reagan, but if we should all agree on one thing, it's that policy has nothing to do with US elections any more.
Meanwhile, Democrats fight tooth and nail to keep anyone who could credibly deliver positive messaging from so much as a nomination on any level of government.