By the spring of 1975, U.S. combat troops had been gone from Vietnam for two years. The country’s long involvement there had ended, the draft had been abolished, Richard Nixon had resigned and the Americans who fought there were engaged at home in an uphill battle to have their service recognized and respected and to redeem promises of veterans care and benefits on which the nation had already started to renege.

But the departure of American troops from Vietnam had not ended the Vietnam War.

About a year and a half after U.S. troops left, North Vietnam embarked on what it thought would be a two-year offensive to overrun the South and decisively win the war. Within just a few months, it was clear that the South Vietnamese forces were crumbling, and President Gerald Ford went to Congress with a request for more than $700 million in aid. Ostensibly, the money was to finance an evacuation of remaining U.S. personnel and some South Vietnamese allies. But Congress feared it was Ford’s way of putting a foot in the door to restart the war.

In a remarkable confrontation on April 14, 1975, the full Senate Foreign Relations Committee went to the White House for a face-to-face meeting with the president. The substance of the closed-door meeting was not made public at the time, but when the minutes were declassified in 1992, there was Ford in black-and-white, admitting the funding was, in fact, intended “to stabilize the military situation.”

Sen. Jacob K. Javits (R-N.Y.) told the president, “I will give you large sums for evacuation, but not one nickel for military aid.” Sen. Frank Church (D-Idaho) warned, “This raises the specter of a new war, thousands of American troops holding on in an enclave for a long period.” First-term Sen. Joseph R. Biden Jr. (D-Del.) said, “I will vote for any amount for getting the Americans out,” but he insisted that money for evacuation and military aid for the South Vietnamese government “are totally different.”

Part of the reason there had been such broad and intense domestic opposition to the war in Vietnam was its sense of strategic futility. We sent hundreds of thousands of Americans into that conflict, backed by the greatest firepower in the world and a willingness to use tactics that shocked our national conscience. But it wasn’t enough, and year after grinding year, it became apparent that nothing was going to be enough.

Before April 1975 was over, South Vietnam would fall, and the image of U.S. helicopters evacuating people off Saigon rooftops would burn into our retinas. But Ford’s request that month to “stabilize the military situation” — to try to salvage an outcome that America had sacrificed so much for — was rebuffed by those confrontational senators.

Congress knew that it was in its power to say no, and it said no. There would be no second coming of America’s war in Vietnam.

The week after that meeting in the Cabinet Room, Ford spoke at Tulane University: “We, of course, are saddened indeed by the events in Indochina. But these events, tragic as they are, portend neither the end of the world nor of America’s leadership in the world. . . . Some tend to feel that if we do not succeed in everything everywhere, then we have succeeded in nothing anywhere. I reject categorically such polarized thinking. We can and we should help others to help themselves. But the fate of responsible men and women everywhere, in the final decision, rests in their own hands, not in ours.”

There is a school of thought that if only America’s war in Vietnam had been longer, bigger and bloodier, it might have ended differently. But what happened after we left makes that hard to believe. We held things together as long as we could, but unless we were going to become a permanent occupying force, and maybe even then, we were only delaying the inevitable.

America is big and rich enough to fight endless wars if there is the public desire and political will to do so. It might constrain everything else we do, but we could find a way. When the will isn’t there to sustain, expand or start wars, however, that is not some inconvenient externality to be sidestepped — it’s integral to our system. Under Article I of the Constitution, Congress is vested with the power to declare war. The debates of the Founding Fathers on the subject made clear Congress got that job instead of the president so that decisions about war and peace would be made not on one person’s say-so but only after vigorous national debate.

Two and a half years after U.S. troops left Iraq, as we have watched Fallujah, Mosul and a swath of additional territory fall to Sunni militants, we are in need of such a debate. That is why it has been maddening to the point of distraction to see the media seek out supposedly expert analysis from people who made bad predictions and false declarations about the Iraq invasion in 2003. Whether they are humbled by their own mistakes or not, it is our civic responsibility to ensure that a history of misstatements and misjudgments has consequences for a person’s credibility in our national discourse.

On Capitol Hill, it’s even worse. After meeting with President Obama last week, congressional leaders emerged in rare bipartisan agreement: All said the president would need no further authorization from Congress for new U.S. military intervention in Iraq. They may agree on that, but they’re wrong: Neither the 2001 Authorization for the Use of Military Force nor the 2002 Iraq war authorization obviously apply in this instance.

Beyond the 60-day window afforded by the War Powers Act, Obama will need overt congressional authorization for additional troops to protect the U.S. Embassy and U.S. personnel, for the several hundred military “advisers” he has just announced, for air strikes by manned or unmanned planes or for any further military intervention.

Obama is plainly reluctant to send troops back at all, let alone to contemplate a larger-scale reengagement. But that doesn’t mean it’s his decision to make. Concerning Saigon in 1975, Ford thought that military reengagement was his decision, and Congress marched to the White House and reminded him that it was not. Concerning Baghdad in 2014, Congress seems determined to march in the other direction.

Obama is right to insist that he will continue “close consultation” with Congress on Iraq going forward, but Congress and the president are both wrong if they think that that consultation consists of Congress being told and not asked what should happen next. Whether we believe the Founding Fathers were right or not to give the responsibility for war and peace to the clamorous Congress, they did. It is an irresponsible constitutional cop-out to pretend they didn’t.

Rachel Maddow hosts MSNBC’s “The Rachel Maddow Show” and writes a monthly column for The Post.