Weld's caustic apostasy handed his enemies a persuasive argument against his fitness for the job--that he's undiplomatic.
The persuasive argument that they handed his enemies was that he was bald.
mnli hypothesis: The persuasive argument that they handed his enemies was that he was bald. premise: Weld's caustic apostasy handed his enemies a persuasive argument against his fitness for the job--that he's undiplomatic.