I think the point was that any cohort with a strong voting record for one party will still have members that vote for another party based on a single issue.

It's not unreasonable to think that someone might agree with the bulk of a party's platform, but disagree on a single issue that's most important to them and can't bring themselves to vote for anyone in that party because of it.

I can imagine guns, abortion, the military, taxes, etc. might fit that bill as someone's single most important issue.

I'm perfectly aware of that. Whether the policy crafters at the DNC realize that is a different story. A lot of people seem to take for granted that only whites vote R so I figured there was no harm in challenging that assumption for the point of my example.