Image copyright Reuters Image caption Mr Trump says his policy of "maximum pressure" led to the summit with North Korea

Following a second surprise visit to Pyongyang by now Secretary of State Mike Pompeo, planning is complete for the historic meeting between President Donald Trump and Kim Jong-un in Singapore on 12 June.

Setting the stage for the meeting, Mr Kim released three Americans from custody. And Mr Trump withdrew from the Iran nuclear deal.

One risk in the US president's decision, which he forecast over several months, is sending the wrong message to the North Korean leader that the United States can't be trusted to honour its commitments.

That's not as big a deal as it appears - there is little trust of Washington in Pyongyang to begin with, and North Korea itself has a long history of cheating.

But Mr Trump's rationale for withdrawal from the Iran deal - it was "defective at its core" because it failed to solve every problem with Iran - establishes a test that Mr Trump will fail in his talks with Mr Kim.

Ironically, Mr Trump is likely to pursue the same kind of narrow strategy with Pyongyang that former president Barack Obama did with Tehran.

If there is a comprehensive solution to North Korea, it will take years to achieve and go through several difficult phases. It will require strategic patience, precisely what Mr Trump failed to display with his Iran decision this week.

In rejecting the Iran deal, Mr Trump equated Iran's right to a civilian nuclear programme as a path to a nuclear weapon. The only acceptable outcome is complete denuclearisation.

Image copyright EPA Image caption Mike Pompeo travelled to North Korea to hold preliminary talks with Kim Jong-un

Under the Trump standard, Pyongyang will need to make a complete disclosure of its entire nuclear complex, dismantle it, give up its missiles and allow nuclear inspectors anywhere, any time access to all military facilities - forever.

North Korea has never done any of these things.

Becoming a de facto nuclear power is the Kim family's only achievement over its seven decade rule. It is hard to fathom why young Mr Kim will be willing to give it away.

And if he is willing to bargain, the price will be high. He won't give away his nuclear and missile capability up front.

'Comprehensive solution not realistic'

Thus, a comprehensive solution is not realistic right now. The best Mr Trump can do is an incremental approach - highlighting the full range of concerns, solving one problem and then building on it, the very approach European leaders recommended - and Mr Trump rejected - in the context of Iran.

The initial meeting between Mr Trump and Mr Kim will last one day, two at most. A reasonable achievement would be a broad framework agreement to guide further negotiations.

North Korea's nuclear complex is significantly larger than Iran's.

If Pyongyang actually agrees to denuclearise - a big if - it will take years to produce a credible baseline disclosure of its actual weapons and research capability, dismantle it and establish an intrusive and permanent verification regime.

Since the nuclear problem is the long pole in the tent, a first agreement could be a peace treaty that formally ends the Korean War.

It would serve as a useful confidence-building measure. As military forces stand down along the Korean border, the risk of an escalating conflict is greatly reduced.

Beyond that, the United States should compel North Korea to cease its illicit cyber activity, from bank thefts to hacks such as the attack on Sony Pictures Entertainment in 2014.

If Pyongyang wants better relations with its neighbours and greater economic investment, it will have to improve its human rights record and government transparency. This would include accounting for Japanese citizens abducted during the Cold War and opening up its vast political prisons.

Image copyright Reuters Image caption Donald Trump said the nuclear accord with Iran was "a terrible deal"

This may actually be the most challenging task for the North Korean regime. Mr Trump said this week that the Iranian people deserve a better government. So do the North Korean people.

The president should say so, but his support of human rights is selective.

Mr Trump dismissed what the Iran deal actually achieved. It halted a march towards yet another war in the Middle East, provided a valuable window into Iran's nuclear activity, reopened an authoritative diplomatic channel between Washington and Tehran, and created time for the two countries to better manage, if not normalise, their relationship.

Any incremental deal with North Korea will potentially carry similar benefits, even if it fails initially to solve every problem between the two countries.

Mr Trump's policy of "maximum pressure" is no match for his grandiose personality. It's more likely than not that there will be an agreement of some kind, which the president will spin as a major foreign policy win.

And what to make of the clear inconsistency between his Iran and North Korea policies?

The Iran deal was flawed because it was negotiated by Mr Obama. By definition, any Trump deal is better, and of course worthy of the Nobel Peace Prize.

P.J. Crowley is a former U.S. Assistant Secretary of State and author of Red Line: American Foreign Policy in a Time of Fractured Politics and Failing States.