WASHINGTON — Behind the blockbuster of a possible diplomatic breakthrough on denuclearization of the Korean Peninsula, the same question that hovered over America’s Cold War dealings with the former Soviet Union now confronts Donald Trump. Can we trust our adversary without verifying its promised positive behavior?

In that earlier confrontation between President Ronald Reagan and Russian leader Mikhail Gorbachev, the collapse of the latter’s regime in a sense resolved the standoff. This time there is no indication that Kim Jong Un’s primacy in North Korea is in any jeopardy. In fact it seems certain to be reinforced by his agreement with President Trump.

But Kim’s track record for reliability is weak, as is his woeful history in the realm of human rights, about which Trump apparently did not confront him in Singapore. The only verification provided was evidence of the American president’s reputation as a wheeler-dealer in achieving a major public-relations coup in the eyes of the world.

Once again Trump boasted in advance that he would do what only he could do, without providing any detail on how it would be done. In purely political terms, the performance undoubtedly enhanced his prospects for re-election in 2020, provided he weathers the Mueller investigation into Russian elections meddling threatening him.

The one cloud over the wide public approval of Trump’s immediate performance in Singapore was the report that he did not consult with his American allies in South Korea in the deal, which would discontinue joint military preparedness exercises with the Seoul regime. The drills have been designed to cope with any North Korean attacks on her southern neighbor.

The North Korean part of the agreement was to allow U.S. verification of the dismantling of missile sites/aimed at South Korea and other American allies in the region, In the Cuban Missile Crisis of 1962, the taking down and shipping back of the Russian missiles was verified by the American navy at sea, and it averted a possible nuclear war 56 years ago.

In evaluating the current deal, much of course will depend on the trustworthiness of a North Korean leader who has been as notoriously unstable as Trump himself has been in his own words and behavior.

The Singapore summit came on the heels of Trump’s continuing effort to shatter elements of the North Atlantic Alliance on our side of the globe. His crude and unwarranted assault on Canadian Prime Minister Justin Trudeau as he went out the door of the G-7 nations meeting in Quebec was a bizarre and reckless prelude to the Singapore summit.

Making an enemy of the young Trudeau, son of a previous Canadian leader, was throwing a sucker punch at a friend, and other members of our Western Hemisphere alliance were disinclined to take it without slugging back. Trump’s characteristic behavior may have been intended to plant his dominance, but it only served further to solidify U.S.-Canadian relations and goodwill.

Even before arrival in Singapore, Trump hung out his bullying calling card along with an insulting declaration that he could “read” Kim in the first minutes of their seance, like a bold poker player taking on yet another witless victim. It was a flashback to another American bullyboy, George W. Bush, asserting he could look into the eyes of Moscow tough guy Vladimir Putin and see a kindred spirit.

Yet once more, Trump as the master practitioner of the art of the deal has delivered in his brief encounter with Kim Jong Un the surface appearance of a miracle-worker, endearing him to his Republican faithful, and probably many Democrats as well.

But will this apparent diplomatic coup be enough to divert the so-called blue wave of opposition party voting to thwart him in the November midterm congressional elections? Once again, these ballot tests loom as the next measurement of voter toleration toward this president’s strategy of governance by self-aggrandizement and self-preservation.

Jules Witcover’s latest book is “The American Vice Presidency: From Irrelevance to Power,” published by Smithsonian Books.