professor at Columbia University and expert on the region. "A military option is not realistic. Even a limited conflict between the U.S. and North Korea would cause tremendous damage and loss of life."

READ China Is the Key to Avoiding Conflict With North Korea ]

Members of the Trump administration have stressed that they are considering military options against North Korea.

National Security Adviser H.R. McMaster said earlier this month that Kim is "going to have to give up his nuclear weapons because the president has said he's not going to tolerate this regime threatening the United States and our citizens with a nuclear weapon." When asked if that included military options, he said Trump has "been very clear about that, that all options are on the table."

U.N. Ambassador Nikki Haleyhad Peru before it.

"So, yes, it's working," Mattis said.

Perhaps the biggest shortcoming of the Trump administration's policy is that it has not specified what negotiations with North Korea would look like or what terms it would have to comply with before talks could begin. Secretary of State Rex Tillerson has said on multiple occasions and repeated on Sunday, "We'll know it when we see it in terms of their seriousness."

Trump also undercut his own threats by tying North Korean aggression to his criticism of Iran, for which the president has said he wants to tear up an agreement limiting its nuclear program, says Vikram Singh, a former top Pentagon official for Asia issues, now a senior adviser at the Center for American Progress. Pyongyang would have no incentive