(CNN) As the US crisis with Iran continues, carrying with it the frightening prospect of a possible military confrontation with Tehran, one question looms large.

If Donald Trump can summit, negotiate and send self-described love letters to Kim Jong Un, one of the world's last true authoritarians -- a man whose country (like Iran) is on America's state sponsors of terror list; who has up to an estimated 60 nuclear weapons; who has launched missiles at Japan and threatened South Korea; and whose record on human rights and abuses against his own people justifiably puts him in the evil category -- why can't he sit down with senior Iranian officials to figure a way out of the current crisis?

The quick answer of course in the context of the current crisis is that having watched the United States withdraw from the 2015 nuclear accord and reimpose sanctions, the most recent of which are directed against the Supreme Leader , Tehran isn't interested in talking, and the administration, tethered to its maximum pressure campaign, isn't all that interested either right now, even though Trump has repeatedly offered to sit down with President Hassan Rouhani without preconditions.

The more intriguing question is why has Trump been able to engage so effortlessly with one authoritarian leader and not with the other? Indeed in his own mind, why is North Korea a more acceptable partner than Tehran? What makes North Korea so different? And what does all of this say about prospects for any serious negotiations with Iran?

Trump's ticket into the history books

Trump is fond of saying that before he engaged directly with Kim, the United States was on the verge of war with North Korea, and through the period of his engagement Kim has not launched long-range missiles or conducted nuclear tests.

Indeed, Trump has given Kim the kind of safe zone from criticism that he's accorded Russian President Vladimir Putin. He is constantly praising him, talking about the beautiful letters he receives from a pen pal who has reportedly ordered the execution of many subordinates and allegedly had his own half-brother poisoned in a Malaysian airport.

Indeed despite two failed summits where expectations exceeded results and the prospects of a third where there seems to be little promise of success, Trump wants to keep the North Korean dream alive

Indeed, he senses that North Korea -- unlike Iran -- would be an unprecedented success, a ticket into the history books, and get him a likely Nobel Peace Prize. And above all, unlike all of his predecessors, it would be his success for having taken the risk to engage Kim personally.

Iran an old and complicated story

Unlike North Korea where Trump has imparted his own unique approach to diplomacy, Iran is an old story fraught, and in Trump's mind complicated by the bungled efforts of others. He spent much time on the campaign trail blasting the 2015 nuclear deal as the worst agreement in human history and using it to hammer Barack Obama. And he pledged to rip it up or at a minimum to renegotiate it.

That the Iran deal was Obama's alone was enough to cause Trump to walk away in an effort to make everyone understand there was a new sheriff in town. As with so many other issues from the Trans-Pacific Partnership to climate to immigration, Trump walked away from everything Obama had touched.

In short, Iran was old business -- Obama's business -- and if he couldn't walk away from the deal immediately, Trump would soon, and he went on to impose a new campaign of maximum pressure.

Unlike North Korea, where he maintained sanctions even while he flattered and gave Kim the benefit of the doubt, with Iran it was all vinegar and no honey. And Iran's behavior outside of the nuclear accord, particularly its efforts to project its influence in the region, gave Trump and his hawkish advisers justification to rationalize leaving the accord and exerting pressure on Iran wherever they could.

Israelis, Saudis and domestic politics

Trump's policies toward North Korea engendered a fair amount of domestic criticism from those who objected to his courting of a brutal authoritarian regime and many who saw his approach as strategy-less and his being bamboozled by a cagey Kim.

In a way, the criticism of Trump's North Korea policy was mitigated somewhat by the fact that North Korea, unlike Iran, was seen to be a serious threat to the United States as a result of its nukes and long-range missiles. But if North Korea was radioactive in US domestic politics, Iran was 10 times more so.

In fact, domestic politics -- opposition among Republicans, conservatives, some Democrats and supporters of Israel -- was a serious constraint on any administration wanting to play let's make a deal with Tehran.

Moreover, unlike North Korea, where Japan and South Korea had serious concerns about dealing and conceding too much to Pyongyang, in the Iranian situation, you had the Israeli factor to contend with and a Prime Minister who was determined to do everything possible -- as demonstrated by his end running the Obama administration and addressing Congress -- to sink the accord. That effort failed, but with the arrival of Trump -- eager to restore US relations with both Israel and Saudi Arabia -- you had a President who played to the anti-nuclear agreement crowd.

Indeed, Trump's opposition to the Iranian nuclear deal was born out of his desire to play domestic politics, and that continues to this day.

In a more normal administration, dealing with both Iran and North Korea -- as different as the situations are -- would be seen as part of a general nonproliferation strategy. And as flawed as the Iran nuclear agreement may have been, parts of it could have been seen as highly functional instruments for dealing with the challenge of North Korea's nuclear program for which the United States has no comprehensive solution.

The irony of the current situation is that despite the constraints on dealing with Iran -- many imposed by Trump himself -- the President still seems to hold open the possibility of engaging Iran, and one gets the sense that if the Iranians, however unlikely, reached out, Trump might respond, despite the views of his hard-line advisers.

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One can only hope that Trump's instincts will prevail; because right now there's no trust, no channels of communication between Washington and Tehran, and every reason to believe that conflict is crowding out what little space exists for some form of diplomacy -- the only conceivable instrument to preempt the march of folly both sides seem intent on following.