But at this lunch on Thursday, Sen. Mitt Romney (Utah) was getting visibly annoyed.

If this is meant to persuade me, Romney told his colleagues, it’s not helpful, according to two officials with knowledge of the exchange. The senator, a near-lone GOP voice in seeking witnesses for the trial, felt as if other Republicans were singling him out…

Receiving testimony from Bolton was a “no-brainer,” he believed, according to an individual familiar with his thinking who, like others interviewed for this story, requested anonymity to speak frankly.

“Here we have somebody who has obviously talked about this issue with the president who may have helpful information,” the person said, summarizing Romney’s thinking. “So why wouldn’t we want to hear from him?”