David A. Andelman, a contributor to CNN and columnist for USA Today, is the author of " A Shattered Peace: Versailles 1919 and the Price We Pay Today ." He formerly served as a foreign correspondent for The New York Times and Paris correspondent for CBS News. Follow him on Twitter @DavidAndelman . The views expressed in this commentary are his.

(CNN) Not every campaign promise is worth keeping. But to please his base, Donald Trump may be about to scrap the main trade pact between the United States and South Korea, the first bilateral treaty he will have terminated as President. Smart? No. Not now, probably not ever.

Isn't this the very moment when we should be doing all we can to support and strengthen South Korea, a nation that is our principal bulwark against a madman who boasts he now has a hydrogen bomb that can destroy civilization? Apparently not, if it means leaving yet another campaign promise to his base unfulfilled.

Donald Trump made that promise as a candidate, back when North Korea was pretty far down on his list of global priorities, and a whole lot of other pledges seemed like better bets.

But one by one, each of his pledges to his base have come to naught. He hasn't managed to " repeal and replace Obamacare ," " build a wall and make Mexico pay for it ," scrap NAFTA or the " total and complete shutdown " of Muslims coming to our shores. But now, at the very worst possible moment, Trump seems hell-bent on touching off a trade war with one of our most critical allies and the very country we most desperately need to support just as it is facing an existential challenge from its arch enemy to the north, which has also threatened to unleash a nuclear Armageddon on America.

Now President Trump has threatened to cut off trading ties with any country doing business with North Korea (which could halt US trade with China). He has also, according to a report in the Washington Post, instructed aides to get ready to withdraw the United States from the free-trade deal with South Korea, even as he and President Moon Jae-in have agreed "in principle" to revise a bilateral treaty that governs the South's ballistic missiles. At least three of his leading advisers on these matters oppose scrapping our trade pact. National security adviser Lt. Gen. H.R. McMaster, Secretary of Defense James Mattis, a retired Marine Corps general, and Gary Cohn, his top economic counselor and former president of Goldman Sachs, are all said to be livid over the prospects of this latest, looming Trump tragedy. But that may not mean much, even though President Trump also said Sunday that he would be meeting with Mattis, his chief of staff John Kelly and other military leaders, ostensibly about the looming North Korea threat.

President Trump apparently also believes the South Korean government needs more spine in its dealings with the North. Or as he tweeted at 7:46 Sunday morning: "South Korea is finding, as I have told them, that their talk of appeasement with North Korea will not work, they only understand one thing!" One wonders how exactly weakening the tent-pole of South Korea's economy is going to put more spine and confidence in South Korea's dealings with the North.

Remember how much the President loves bilateral trade agreements and hates big multinational pacts that he blames for giving away the store and destroying American jobs? Well, it's true, South Korea does ship more than $20 billion more goods to the United States than we send its way each year. But that includes a whole lot of Samsung televisions and smartphones, and cheap cars, that if both countries slapped on major duties would cost American consumers a whole lot more than they're paying now. Not to mention the output of American farms, whose exports to South Korea have soared, with beef exports alone more than doubling in the past six years. And then there's the $23 billion in investments South Korea has made in the United States. How many of these might now be put at risk? How well is all this going to go down in middle America?

It's worth remembering, too, that the new South Korean government is barely four months old, with liberal President Moon Jae-in coming to power after the arrest and impeachment of his predecessor amid a massive corruption scandal. Moon Jae-in said during his campaign that some accommodation with North Korea was essential and opposed deployment of the THAAD, or Terminal High Altitude Area Defense System, by US forces in South Korea. In the wake of North Korean missile and nuclear tests, however, he has now asked American permission to augment his nation's own missile forces and agreed to at least temporary deployment of a full THAAD battery in the South. Any effort to cut trade relations by the United States could only be viewed most darkly by this South Korean leader who has only just begun coming around to a more appropriate view of how the North should be treated.

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The end of the Trans Pacific Partnership trade pact has left China very much in the driver's seat across much of Asia, and South Korea clinging to one reed still left to its prosperity — the trade pact with America. Now President Trump seems poised to snatch this from its outstretched hand, effectively ending with one stroke what is left of our amicable relations with South Korea.