People briefed on the meetings said American negotiators found it difficult to make significant headway with the North Koreans, in part because the White House did not back them up in taking a hard line.
In his public statements, Mr. Trump has shown gradually greater flexibility toward North Korea, saying he viewed its disarmament as a “process,” rather than something to be done all at once, and disavowing the phrase “maximum pressure,” after making it the centerpiece of his policy.
Mr. Pompeo took issue with a report in The New York Times that Mr. Trump would be handicapped in the negotiations because of a lack of scientists on his negotiating team. He said the government could draw on the expertise of dozens of people with doctorates in nuclear, chemical and biological weapons.
“Any suggestion that the United States somehow lacks the technical expertise across government, or lacks it on the ground here in Singapore, is mistaken,” Mr. Pompeo said.
Some foreign-policy experts said the breakdown at the Group of 7 meeting would play to North Korea’s advantage, since Mr. Trump can ill afford two failed summit meetings, back to back. The president has consistently predicted success, even as his definition of that has grown foggier.
The unraveling of the gathering in Canada increases the North Korean leader’s incentive to “up his asks and limit his compromises and for Trump to do the opposite,” Richard Haass, the president of the Council on Foreign Relations, said on Twitter, adding, “Hardly the ideal context.”