Attacking Hillary Clinton over what he criticized as her overly interventionist instincts, Mr. Johnson pointed to the hundreds of thousands of Syrian civilians killed by forces loyal to President Bashar al-Assad, as well as civilian deaths caused by the American-backed coalition, and said Mrs. Clinton, the former secretary of state, bore at least partial responsibility.

But when pressed four times on whether he saw a moral equivalence between deaths caused by the United States, directly or indirectly, and mass killings of civilians by Mr. Assad and his allies, Mr. Johnson made clear that he did.

“Well no, of course not — we’re so much better than all that,” Mr. Johnson, a former New Mexico governor, said sarcastically. “We’re so much better when in Afghanistan, we bomb the hospital and 60 people are killed in the hospital.”