Cha served as director for Asian affairs on the White House National Security Council in the George W. Bush administration. The Korean-American is currently the Korea chair at the Center for Strategic and International Studies in Washington.

"North Korea, if not stopped, will build an arsenal with multiple nuclear missiles meant to threaten the US homeland and blackmail us into abandoning our allies in Asia. ... These are real and unprecedented threats. But the answer is not, as some Trump administration officials have suggested, a preventive military strike," he said.

"But a strike (even a large one) would only delay North Korea's missile-building and nuclear programs," he added. "A strike also would not stem the threat of proliferation but rather exacerbate it, turning what might be a North Korean moneymaking endeavor into a vengeful effort intended to equip other bad actors against us."

Cha worried that any such military action could expose millions of South Korean people but also many American soldiers and their families to a barrage of North Korean artillery at a time when there are "no similar active defenses" as those installed in Japan.

"The president would be putting at risk an American population the size of a medium-size US city -- Pittsburgh, say, or Cincinnati -- on the assumption that a crazy and undeterrable dictator will be rationally cowed by a demonstration of US kinetic power," he said.

He, instead, called for more pressure on the North and cooperation with partner countries to force Pyongyang to give up its nuclear and missile ambitions, saying it could provide similar effects as those from a "limited" strike without causing "self-destruction."

"The Trump administration must continue to strengthen the coalition of UN member states it has mustered in its thus far highly successful sanctions campaign," he said.

"The United States must significantly up-gun its alliances with Japan and South Korea with integrated missile defense, intelligence-sharing and anti-submarine warfare and strike capabilities to convey to North Korea that an attack on one is an attack on all."

Cha said that it is also necessary to build a "maritime coalition" around the North, while making sure China and Russia block its proliferation attempts by using their borders.

"Lastly, the United States must continue to prepare military options. Force will be necessary to deal with North Korea if it attacks first but not through a preventive strike that could start a nuclear war," he noted. (Yonhap)