Trump’s unraveling of the post-war order accelerated this week when he announced a willy-nilly pullout from Syria, leaving in the lurch scores of allies who participated in the campaign against the Islamic State, throwing our Kurdish partners to the wolves, isolating Israel, and giving Russia and Iran free rein in the Middle East. Then word emerged that Trump is ordering another hasty withdrawal, from Afghanistan. Trump’s defense secretary, retired Gen. Jim Mattis, resigned in protest of the president’s estrangement of allies and emboldening of Russia and China.

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The TV series “The Man in the High Castle” imagines a world in which Nazis won World War II. But we don’t need an alternative-history show to imagine a Soviet victory in the Cold War. We have Trump.

Mattis, in his memorable resignation letter (a bookend to George Kennan’s “long telegram” of 1946) wrote: “We must do everything possible to advance an international order that is most conducive to our security, prosperity and values, and we are strengthened in this effort by the solidarity of our alliances. Because you have the right to have a secretary of defense whose views are better aligned with yours on these and other subjects, I believe it is right for me to step down from my position.”

Mattis spelled out the views of his that are apparently not “aligned” with Trump’s: “treating allies with respect,” believing in the 29 NATO democracies (Trump has repeatedly raised questions about NATO’s utility); respecting the 74-nation “defeat-ISIS coalition” (now to be abandoned in Syria); and recognizing threats from China and Russia, which “want to shape a world consistent with their authoritarian model . . . at the expense of their neighbors, America and our allies.”

Republicans now profess to be alarmed. Senate Majority Leader Mitch McConnell (R-Ky.), who has enabled Trump at every step, says he’s “particularly distressed.” Sen. Lindsey O. Graham (R-S.C.) sees “chaos.” But that is too little, too late. Turkey says it will postpone an invasion of Syria as U.S. forces leave — the better to “bury” our Kurdish allies. And Russian President Vladimir Putin exults: “American troops should not be in Syria and have been there illegally.”

Indeed, a Soviet leader hardly could have outlined a better scenario than Trump has created for Putin:

A rift between the United States and NATO allies over the future of the alliance.

A U.S. demand that Russia be returned to the Group of Seven , as Russia continues provocations in Ukraine.

A U.S. president abandoning human rights, accepting Saudi Arabia’s murder of a U.S.-based journalist and embracing repressive leaders around the globe.

A U.S. president creating a rift with Europe over Iran (the nuclear agreement) and climate change (the Paris accord).

A U.S. president embracing as “very honorable” North Korea’s brutal dictator without any tangible concessions on nuclear weapons.

A U.S.-launched trade war that, the Federal Reserve said this week, is partially responsible for cooling worldwide growth.

Lost confidence among Americans in elections, the Justice Department, the FBI, the courts and the free press.

And the loss of a bipartisan consensus against the Russian threat. Forty percent of Republicans called Russia an ally or friend in a Gallup poll, up from 22 percent in 2014.

Why has Trump squandered so much for so little? Maybe it’s because, during the 2016 campaign, Russia was privately negotiating a business deal in Moscow with him and releasing stolen documents that hurt his Democratic opponent. (Meanwhile, Trump was praising Putin and his campaign was softening the GOP platform on Russia.)

Whether special counsel Robert S. Mueller III concludes there was a quid pro quo, Putin clearly has benefited from Trump’s presidency.

In Helsinki, in front of the world, Trump accepted Putin’s word over that of U.S. intelligence agencies. Trump has chafed at aides’ insistence on Russia sanctions, and the few who could resist Trump’s pro-Putin instincts are gone: H.R. McMaster, Rex Tillerson, John Kelly and now Mattis.

Generations of Americans paid any price and bore any burden, from Berlin to Saigon to Havana. Now, 29 years after the wall fell, Trump is handing Moscow the Cold War victory it could never win.

Twitter: @Milbank