We often find occasion to interact with people who are so opposed to our political views, they will challenge your audacity to even hold that view. When you find yourself in that situation, it is entirely possible that you could be speaking to someone who, if given a respectful, thoughtful response, might be appreciative enough to change their minds or to, at least, consider an opposing view.
If Kamala Harris is your choice, you might consider studying and even memorizing this response from a Harris supporter who saw him in Cosco wearing a Harris t-shirt and challenged him on how he could support her:
Democracy High is interested in hearing of other examples of model responses for dealing with similar situations.