Maybe. but remember, Cain was the farmer, Abel the shepherd.
Cain, like all farmers worked hard to produce very little "profit" he could offer to God.
So Cain was jealous of his "easy-life" shepherd brother.
But I'd say, up to that point they are both producers, which means in today's terms, Republicans.
Now Cain decides to win God's favor, not by producing more, rather by eliminating Cain's competition, Abel.
That might make Cain a corrupt capitalist, or swamp critter, not to be claimed by either party today, though perhaps tolerated more by some than others, depending on which received more campaign contributions.
But God would have none of it, punished Cain, though also protected him so Cain moved to new land & built a city.
Now, so far as I can see, Cain is a normal human being who worked hard, grieved & sinned when others seemed to live an easier life.
But here's no doubt God still loved Cain (and Cain loved God!) despite Cain's great sin.
What would make Cain a Democrat, would be, first & foremost if he declared God had no power over him, because for all Cain knew, God did not even exist.
Next, Cain does not outright kill Abel so much as he taxes Abel to death and uses Abel's tax money to support Cain's jobless friends, the Nephilim.
Then Cain opens the gates of his new city to all comers taxing Abel ever more to support them.
But none of that happened, Cain was still loved by God and in time became the ancestor of many.
So I'm thinking Cain's was a forgiven & redeemed soul, and Cain himself a producer, a builder and in time a good citizen.
In short, in time a solid Republican.
You disagree?
It would be easier for Cain to qualify as a Democrat Candidate being a known murderer.
If he tried to run as a Republican, the media would trash him.