Who lost Korea? That question may sound premature but it may not sound so for long. Not if the newly elected president of the free Korean republic, Moon Jae-in, does what he has been threatening. He is a leftist human rights lawyer who campaigned on the idea of entente with the communist north. And on distancing South Korea from the United States that gave on the field of battle more than 33,000 of its own sons to secure Korea’s freedom. Other than the fact that an election was held, it’s hard to put a positive spin on the outcome.

For one thing, Mr. Moon may well accede to the presidency on 40%, if that, of the vote. That’s the tally for Mr. Moon as we go to press. It looks like Ahn Cheol-soon of the centrist Peoples’ Party tallied 21% of the vote, and Hong Joon-pyo, of the right of center Liberty Party, drew 25%. There’s nothing wrong with a plurality, but the fact is that parties well to the right of the winner got something nearly one and a half times the winner’s vote. This is the basis on which Mr. Moon is likely to launch his détente with the communists.

How, though, did this happen? Our own thoughts go back at least to the early years of the Obama administration, when, in 2010, the Group of 20 held its summit in Seoul. What a disaster. “Obama’s Economic View Is Rejected on the World Stage,” was the headline in the pro-Obama New York Times. “European and Asian powers have had it with being lectured by the U.S,” is the way it was put in another pro-Obama newspaper, the Daily Beast, which reckoned a letter Mr. Obama wrote to his foreign counterparts was fated to “make things worse.”

“Mr. Obama,” we said in an editorial at the time, “couldn’t even fetch a free trade agreement with, in Free Korea, a host country that has been running newspaper ads thanking America for 60 years of support.” He used the words “must” or “should” 11 times — to no avail. There have been some ups and downs in Korean policy since that disaster (a trade deal was finally inked in 2012), but it’s hard to lay to coincidence that all this is happening at the end of eight years of an Obama administration that has made retreat from the world stage and a reduction in our military a hallmark of its policy.

Not that Donald Trump ran a campaign for the kind of trade deal that would thrill Free Korea. We get that down to the ground. Then, again, too, Hillary Clinton was a camp follower of Mr. Trump in campaigning against the Trans Pacific Partnership that President Obama couldn’t secure. Mr. Trump, though, is doing the right thing beginning to reverse the decline in our military budget. He also has done the right thing in moving to Korea an armada and other assets, like the anti-missile system known as Terminal High Altitude Air Defense.

We don’t mind saying we’d had hopes that Mr. Trump’s saber rattling might embolden the South Koreans to swing behind the hardline parties. For a while it looked like they might, too. Then, on May 1, Mr. Trump told Bloomberg News that he’d be “honored” to meet with North Korea’s dictator, Kim Jong Un. He did say he would do it only “under the right circumstances,” but what could they be? Nothing but a departure of two generations of bipartisan refusal by American administrations to receive the North Korean communist thugs in direct talks.

We wouldn’t want to make too much of Mr. Trump’s blunder on that head, but we wouldn’t want to fail to mention it. The net of the past decade is that the only Koreans who can vote on anything have voted to put some distance between themselves and America and seek an entente with one of the cruelest oppressors ever put a heel on a Korean throat. The newswires report that Mr. Moon will meet with President Trump before any of this gets underway. Maybe Mr. Trump can pull a miracle out of this hat so that he won’t be known as the president on whose watch Free Korea was lost.