His comments could also fuel further skepticism among some Libertarian voters who view Mr. Weld’s right-of-center years as governor with suspicion. They could also inflame criticism that he is a de facto stalking horse for Mrs. Clinton, the Democratic front-runner for the nomination.

Mr. Weld gave a single-word response about whether Mrs. Clinton was a good secretary of state: “Yes.”

He was equally succinct when asked if her use of a private email server, now the subject of an F.B.I. investigation, was a legitimate issue.

“No,” said Mr. Weld, a former prosecutor, adding that he had read of no evidence that would clear the bar for criminality. “I think it’s a nonstarter.”