It's time to get really concerned about a renewal of fighting on the Korean peninsula. There was only an armistice, not a peace agreement, that ended the fighting in 1953.
We have long been used to bombast from the Korean media and its leader. Now the American president is trying to match the explosive rhetoric. What makes Trump's comments more threatening is that they come at a time when U.S. public opinion is becoming increasingly hawkish. A quickie CBS poll is "uneasy " about the Korean situation, and about Trump's ability to handle it. Some 29% favor "military action now." A more substantial survey by the Chicago Council on Global Affairs finds 40% of Americans favoring airstrikes on North Korean nuclear production facilities and 28% favor sending U.S. troops into the country to destroy its nuclear facilities. Only 11% of respondents are willing to accept a nuclear-armed North Korea.
Although large majorities of 68-78% prefer sanctions against North Korea and China to try to end the nuclear programs, that approach has regularly failed in the past. I personally favor Bob Gates' proposal for joint US-Chinese inspection of a North Korean commitment to freeze its existing missile and warhead programs in return for US diplomatic recognition and other normalization. That's the best possible deal at the moment. But it would mean accepting a world where DPRK had a modet but real nuclear capability, a very tough stance for any US president to accept.