There is more to this than A/B testing.
“If you aren’t for Trump, then you’re for Clinton” is a cheap rhetorical ploy. I’d write that any thinking adult would be ashamed for falling for that kind of sixth-grade debater’s stratagem, but a Republican electorate capable of choosing Donald Trump as its standard-bearer is incapable of shame.
The angry insistence — him or her! — is, for the moment, mainly an attempt to forestall further criticism of Trump. That criticism consists of stating a fact that is not a matter of degree but a binary proposition, a yes/no question. It is not that Trump is less mentally stable than Mrs. Clinton (probably true) or that he is more dishonest than Mrs. Clinton (difficult to say) or that he might do even more damage to the republic, or any other point of comparison between the candidates.
The issue, instead, is this: Donald Trump is unfit for the office.
He is unfit for any office, morally and intellectually.
A man who could suggest, simply because it is convenient, that his opponent’s father had something to do with the assassination of President Kennedy is unfit for any position of public responsibility.
His low character is disqualifying. His personal history is disqualifying. His complete, utter, total, and lifelong lack of honor is disqualifying. The fact that he is going to have to take time out of the convention to appear in court to hear a pretty convincing fraud case against him is disqualifying.