There is an interesting catch to this argument, which is that in a human body we can eliminate pain by using general anesthesia or nerve blockers. Locally the body still reacts to damage but the actual person doesn’t experience any pain because it isn’t communicated to their consciousness. If we accept that being unconscious precludes experiencing pain then it follows that consciousness is a pre-requisite for pain.
On the other hand if it’s still unethical to inflict damage on a living thing without consciousness then is it unethical to operate on a sedated person even though they don’t consciously experience pain?
At this point the downside is that if that debate is the best he can do then he’s absolutely going to lose.
If he does make it to Election Day without dropping out or dropping dead then yeah we may as well vote for him, but that seems like a terrible position to be in.