Former U.S. officials and other experts said the United States essentially had two options when it came to trying to curb North Korea's fast-expanding nuclear and missile programs — negotiate or take military action.
Neither path offers certain success and the military option is fraught with huge dangers, especially for Japan and South Korea, U.S. allies in close proximity to North Korea.
The Republican president-elect complained in a separate tweet that China, North Korea's neighbor and only ally, was not helping to contain Pyongyang — despite China's support for successive rounds of U.N. sanctions against Pyongyang.
While many critics, including within President Barack Obama's administration, agreed China could press North Korea harder, the State Department said it did not agree with Trump's assessment that China was not helping.
Experts said Trump's tough stance toward Beijing on issues from trade to Taiwan could prove counterproductive in securing greater Chinese cooperation.
James Acton, co-director of the Nuclear Policy Program at Washington's Carnegie Endowment for International Peace think tank, said that with his North Korea tweet, Trump had drawn a red line he could later be judged by, like Obama's 2012 warning to Syria over the use of chemical weapons.
"This was a foolhardy tweet for Trump to send given the enormous challenges of constraining North Korea's nuclear and missile programs. I think this could be something that comes back to haunt him."
U.S. officials, who did not want to be identified, said that if ordered, the U.S. military had three options to respond to a North Korean missile test — a pre-emptive strike before it is launched, intercepting the missile in flight, or allowing a launch to take place unhindered.
One official, who did not wish to be named, said there were risks with pre-emptive action, including the possibility of striking the wrong target — or North Korean retaliation against regional allies.
Arms control expert Jeffrey Lewis questioned whether U.S. missile defenses could shoot down a test missile, absent a lucky shot, and said destroying North Korea's nuclear and missile programs would be a huge and risky undertaking.
Lewis, at the Middlebury Institute of International Studies in Monterey, California, said it would require "a large military campaign ... over a fairly substantial period of time."
He noted that North Korea's main nuclear and missile test sites were on different sides of the country and factories that supplied them were scattered over several provinces.
"There's a warren of tunnels under the nuclear site. And an ICBM can be launched from anywhere in the country because it's mobile. You might as well invade the country," Lewis said.
Republican U.S. Senator Cory Gardner, writing on cnn.com, said he hoped Trump's administration would impose "secondary sanctions" on firms and entities that help North Korea's weapons programs, many of which were in China.