How do you solve a problem like Kim Jong Un? The solutions proposed thus far on the campaign trail are less than promising.

For example, both Democratic candidate Bernie Sanders, a U.S. senator from Vermont, and Republican hopeful Donald Trump have suggested outsourcing the challenge of dealing with North Korea to China.

That’s magical thinking. The notion that Beijing can or will dictate marching orders to Pyongyang has proved a chimera time and time again.

The administration of President Obama flailed around for years before finally settling on its answer to the Kim problem: Force the North Korean strongman to the negotiating table by toughening sanctions on his rogue regime.

The administration re-embraced that approach just a few months ago. On the one hand, the approach represents a refreshing change of pace. For four years, Obama resisted calls for tougher sanctions, insisting that North Korea was already the most heavily sanctioned country on the planet.

It wasn’t. Zimbabwe had more entities listed for sanctions, and there were lots of loopholes that let Pyongyang do business.

Now, from the campaign trail, Hillary Clinton has indicated that, should she succeed Obama, her North Korean policy would be more of the same: tightening sanctions until Kim comes to the bargaining table.

Certainly there’s utility in that approach. Tougher sanctions would further hamstring the regime, leaving it with less cash to build more nuclear weapons and further develop its intercontinental ballistic missiles.

But the goal of U.S.-North Korean policy should be to get Kim to give up his nukes, just as Libyan dictator Moammar Gadhafi did in 2003. And to accomplish that, tougher sanctions are not enough.

We know this because we’ve tried it — while Clinton was secretary of state. It failed spectacularly.

From 2009-2011, the official American policy was to ramp up pressure on North Korea. The then-new Obama administration bragged its sanctions were far tougher than anything the previous administration of George W. Bush had applied. The White House also made clear that it had no interest in talking until Pyongyang showed a better attitude.

A two-year attitude adjustment period ensued, and then the administration started talks — pretty much the same strategy Clinton is proposing now.

This led to the February 2012 Leap Day Agreement. Under this deal, North Korea agreed to halt its nuclear and missile tests and to allow International Atomic Energy Agency inspectors back into the country.

In return, the U.S. and its partners would send 240,000 tons of food aid. The agreement was no game-changer. It didn’t eliminate Kim’s nuclear menace. And it didn’t last.

After banking the food, Pyongyang resumed testing its nukes and missiles. Today, analysts believe North Korea has a functioning missile with intercontinental range — one that can be tipped with a functioning nuclear warhead.

The spank-and-negotiate strategy won’t work for one simple reason. It’s called asymmetry of interest. The last thing Kim’s going to bargain away is the thing he values most: his nuclear threat.

The Iran deal is an object lesson. Tehran happily negotiated an end to sanctions while giving up nothing of importance to the mullahs. The deal never threatened to end the mullahs’ nuclear weapons program — it just calls for a 10-year, time-out period.

As the Iran deal unravels, it’s becoming increasingly clear that the regime remains a troublemaker — one whose nuclear ambitions have not been effectively curbed.

Sanctions alone cannot solve the Kim problem, though they ought to stay in place and stay tough until North Korea becomes a different country.

Meanwhile, the U.S. needs to get busy neutralizing the threat by building missile defenses, modernizing its nuclear arsenal, pursuing the nonproliferation initiative and arranging a strong conventional military deterrence in Asia.