Everything I have read about late undecided voters (and they are not a large or wide demographic) affirms that they tend to be disengaged, uninformed, antagonistic toward the institutional parties, and politically/ideologically incoherent. There is probably no identifiable targeted way to pander to such a diverse and inconsistent group, and arguably politicians shouldn't try.
Here is a fine representation of an archetypical such (at least as often non)voter.
https://twitter.com/LRonMexico/statu...53743912697856
To build off what I was saying earlier about a Sanders nomination, with many such you may enjoy a favorable reaction to Sanders' contrarian image, or alternatively even an effect like 'Sanders calls himself a socialist but he isn't extreme left like the Democrat Party.' Who knows, but don't go down the garden path too far thinking about it.
Bookmarks