Donald Trump has a simplistic view of the problems facing the United States (both domestic and foreign). And that view that our problems are simple to solve extends to the threat of North Korea having nuclear weapons and developing ballistic missiles that can carry those nuclear bombs.
Trump thinks all we have to do is cajole and/or threaten (with economic sanctions) China into taking care of North Korea -- and if China doesn't do that, then bombing North Korea will solve the problem. That view was also expressed by the vice-president in the last couple of days. And sadly, some politicians on both the left and right who normally have sensible views (like Bernie Sanders and John McClain) are succumbing to Trump's simplistic assessment.
The problem is that most issues are complicated, and cannot be solved with simplistic solutions. And that is true of the North Korean issue. Other countries do not see the issue the same way Americans do, and some of those countries (China and North Korea) are not prone to give in to American threats.
This does not mean the problem can't be solved -- only that the simplistic solutions of threats and military strikes are not likely to work. As past presidents have known, this is a problem requiring a diplomatic solution -- and diplomacy can be complicated and time-consuming, but it works.
These paragraphs from Mark Sumner at Daily Kos give us a glimmer of how complicated the North Korean issue is:
Kim Jong Un could be singularly reluctant to cooperate for a simple reason. The Taliban didn’t have any nuclear weapons or long range missiles. Afghanistan was bombed and taken over. Saddam didn’t have any nuclear weapons or long range missiles. Iraq was bombed and taken over. Assad doesn’t have any nuclear weapons or long range missiles. Syria was bombed and … stay tuned. That North Korea massively accelerated nuclear ambitions after 2001 and exploded its first test blast in 2006 is no coincidence. US policy often seems to treat North Korean leaderships as unreasoning blowhards who understand that giving up the weapons will lead to being left alone. But that leadership appears to believe exactly the opposite — surrendering the weapons, or even failing to continue with development, is something they see as tantamount to handing over their nation. As futile, and even nonsensical, as North Korea’s bristling, blatant disregard for international agreements, and finger-on-the-trigger actions may seem, the leadership there could well be sincere in the belief that they’re taking the only route to secure the continued existence of the entire regime. That’s not a formula that leads toward easy resolution. China’s position is also not so easily described. On the one hand, North Korea represents a tiny part of China’s trade, and having a poor, unstable, nuclear-armed neighbor may seem like the sort of situation where helping disarm that neighbor would be a great idea. On the other hand, North Korea holds an out-sized position in China’s recent history. While America sees the Korean War as an ugly, unresolved conflict that represented only the opening act in a East-West conflict—a conflict so drowned out by what came later that it’s been called “the forgotten war”—that’s not how it’s seen in China. For China, the Korean conflict was the first opportunity for new communist government to challenge nations that had treated it as an afterthought to that point. After being invaded, defeated, and disrespected during World War II, China places a huge amount of pride behind the idea that, just a few years later, they challenged the most powerful military in the world and fought it to a draw. Even if the Korean War didn’t end in the south being completely overrun, the Chinese version of the story treats the war as a huge victory. There are six decades of mythology behind the relationship of North Korea and China, and even if the government is ready to alter that story, it’s unlikely to happen overnight. Or over cake.