They said “no” because to them, the most important thing is blaming Kamala for whatever happened in some way. They’re disagreeing with you because you didn’t do that, and trying to correct you on it.
You blamed the voter, which was the right response. I would expand that to include blaming the obviously Russian-influenced campiagn, however it happened, that convinced this person that Ukraine was a hugely important issue in this campaign in this particular bizarre way.
We can give some blame to Kamala for her messaging, sure. But the thing you didn’t do, that made them say “no,” was redirect the whole conversation into a conversation about how it’s all Kamala’s fault and nothing else.