The author of this editorial supports his argument validity

argument validilty

D) by demonstrating through example how one state can unfairly dominate another state's votes in the Electoral College.

Explanation:

The author supports his argument's validity by demonstrating through example how one state can unfairly dominate another state's votes in the Electoral College. Specifically, the author shows how one person in California can overrule the votes of hundreds (even thousands) of people in several other states.