But it spurs worries that Washington might also lower its sights and settle for results falling short of complete denuclearization, which would effectively amount to recognizing a nuclear North Korea as long as it does not pose threats to Americans, the worst case scenario for South Korea.

DePetris argued that complete, verifiable and irreversible denuclearization of the North is a "fantasy."

"We need a completely different metric for success," he said in the article carried by Fox News website. "Ultimately, the paramount US policy objective with respect to North Korea is not denuclearization, but peace, security, and predictability on the Korean Peninsula."

He also argued that next week's summit can be a success "only if the president focuses less on Pyongyang's nuclear dismantlement and more on creating a more amicable and predictable security and peace regime on the Korean Peninsula."

"Indeed, if Trump leaves Vietnam with a mutual commitment from Kim to turn the page on nearly 70 years of hostile relations between Washington and Pyongyang, the president would have accomplished something his predecessors have not," he said.

The North could agree to "some partial, reversible" denuclearization steps, but the White House should not expect more than that in the current security environment, the expert said.

"Why, after spending untold billions of dollars over a quarter-century researching, developing, building, and modifying a nuclear and ballistic missile capability at considerable cost to its economic development, only to have a change of heart?" he said.

"Given North Korea's weak position compared to its more wealthy and militarily powerful neighbors, Kim Jong Un would be downright crazy to do so," he added.

DePetris also took note of South Korean President Moon Jae-in's drive to make peace with the North, saying the initiative has demonstrated to the world "how beneficial reconciliation with the North can be to the security of the region." (Yonhap)