Which technique involves a speaker undermining a competitor's qualifications instead of presenting their own strengths?

The technique in question is one where a speaker attacks or undermines a competitor's qualifications rather than focusing on their own merits or strengths. This method is known as an Ad Hominem attack. It shifts the focus from the actual argument or qualification of the individual to personal characteristics, motives, or actions. This kind of reasoning is often seen in debates and discussions, where one participant attempts to discredit another by casting doubt on their credibility or character instead of addressing the core issues or strengths relevant to the discussion at hand.

In contrast to the other techniques present in the question, an Ad Hominem attack does not provide constructive evidence or reasoning; instead, it serves to distract or detract from the substantive debate on qualifications or abilities. This is why this particular technique is widely recognized as a logical fallacy in both academic and public discourse.