Well, lemme try and come up with a guess for how they'd come across to the electorate:
1. Lion El'Jonson:.....Honestly, drawing a bit of a blank here.
3. Fulgrim: If San Francisco was a person, it would probably be him. Which is why no one outside of Cali would vote for him.
4. Perturabo: The only comparison I can come up with is "Hilary, but instead of no-charisma he has anti-charisma".
5. Jaghatai Khan: Extremely capable as an individual, but would likely struggle to work with the rest of the political power structure.
6. Leman Russ: Video surfaces partway through campaign of him drunkly burning down a Denny's.
7. Rogal Dorn: "We're going to build a wall and make us pay for it!"
8. Konrad Curze: No.
9. Sanguinius: Also drawing a blank here.
10. Ferrus Manus: Technocrat with so-so people skills.
12. Angron: Video surfaces partway through the campaign of him burning down an orphanage.
13. Roboute Guiliman: Presents brilliant, highly effective plan to fix everything, but no one is willing to sit through his thousand page power presentation to see what it is. Wins anyway for poorly explained reasons.
14. Mortarion: Take Perturabo, but dump the part about having some kind ruthlessly effective policy, and even more anti-charisma.
15. Magnus the Red: Hilary 2.0.
16. Horus: Liked by everyone.
17. Lorgar: Would easily win the religious vote, if not for the fact he champions a faith that no one else believes in.
18. Vulkan: Drawing a blank as well. Like, he's got the whole "caring, man of the people thing" going on, but I've never read a book with him in it so I'm not sure how that comes across.
19. Corvus Corax: Same deal.
20. Alpharius: Could probably make a go for the general and do well, but instead sets up a complex web of third parties, support for other canidates, and various other excessively clever schemes to try and play kingmaker, which ends up backfiring somehow.