President Biden will no doubt get a warm welcome from the communist heavies greeting him when he arrives on Sunday at Vietnam. The visit follows the Group of 20 parley in India. It is expected to focus on the threat from China and the prospects for an expansion of the computer chip industry. Good luck, we say. We can’t help but think that the Vietnamese communists have a special place in their hearts for Mr. Biden.

For it turns out that Mr. Biden is the only American president to have voted in the Senate to cut off military aid to Free Vietnam in its most desperate days. That was in April 1975. It was the culmination of a long train of powder. There is plenty of blame to go around. It involved more than one vote. They were the votes by which the Democrats abandoned Indochina to communism for 50 years and counting.

No doubt it will be said that no one cares any more about what happened in 1975. It happens, though, that we do. It will be said that America had every right to pull its GIs out of Vietnam. Then again, too, 1975 wasn’t about saving our GIs. The last GI — Master Sergeant Max Beilke — left Vietnam in 1973. There were no American combat troops in Vietnam in 1975. What happened then was that we let our ally be conquered.

It was one of the great hinges in American history. On the one hand were the Republicans, led by President Ford and Secretary Kissinger, prowling the halls of Congress begging the Democrats to give our ally the military materiel they needed to survive. On the other hand were the Democrats preparing to force our abandonment of the ally they took us to war to support. 

This came to a head with the seating in 1973 of the 93rd Congress. That is when Mr. Biden began his years in the Senate. Though his country was at war, he’d shown no interest in serving in it himself — and took five deferments as his contemporaries were getting drafted. In the Senate he drew an assignment to the Foreign Relations Committee, and voted, like most senators from his party, against sticking with our allies. 

By then the Democratic newspapers had already published the Pentagon Papers and the Watergate Scandal had erupted, weakening Nixon’s presidency and eventually forcing him from office. Watergate became, for many, a strategy for cashiering the last president who might have saved Free Vietnam. Nixon was long gone, though, by the spring of 1975, when Congress caved in a flurry of activity that doomed South Vietnam.

There was one last sliver of hope when — Congressional Quarterly reminds us — the Senate voted for contingency  funds for humanitarian assistance for South Vietnam and Cambodia. It would have allowed the President, as CQ summarized it, “to use the armed forces in the withdrawal of U.S. citizens and their dependents and foreign nationals from South Vietnam.” 

Senator Biden was among three Democrats who refused to vote even for contingency funds to make sure Americans got out. Without him the measure did pass the Senate, but it was rejected by the Democrats in the House. So Vietnam, abandoned by Congress, fell at the end of April — one of the darkest days in American history and one of which the future 46th president of the United States was an author.

None of this is going to come up, we’d guess, when President Biden sits down with his hosts in the Socialist Republic of Vietnam. Yet the Vietnamese heirs to Ho Chi Minh and his regime will know exactly who Mr. Biden is and exactly where he was when America abandoned the Free Vietnamese regime they were trying to defeat. So what will they make of it if Mr. Biden asks them for support against Communist China?