Critics of the decision to withdraw our combat troops from Afghanistan should have to answer a question: What should we do instead?

How long do they believe America should stay to make sure that our side remains in power? The Wall Street Journal has editorialized that we owe both Afghanistan and Iraq the same commitment that we made to South Korea and Europe. That commitment has lasted 70 years in Europe and 62 in South Korea. Do the hawks believe that we should be willing to stay for decades, with thousands of American combat troops costing tens of billions a year, until we are sure our allies can win a civil war?

And be clear that we are talking about combat troops. I have spoken to those who have served as American military “advisers” to the Afghan army. Their job is to accompany Afghans into battle and help them wage it. The notion of an adviser standing by giving instructions while a war is going on is, of course, preposterous. And the recent bombing of a hospital is further confirmation that we are playing a full combat role. (In an example of bootstrapping, we are told that the way to avoid future mistakes is to make sure there are Americans on the ground when air power has to be called in.)

Admittedly, if President Obama were to proceed with his plan to withdraw significant American troops by the end of next year, there is a danger that the bad guys will take back the country. I deeply regret that on behalf of the Afghans, but the notion that America, having intervened to establish a particular regime, is somehow obligated, morally or strategically, to stay there forever to make sure that regime never loses to superior internal forces is gravely mistaken.

First, to the extent that our major strategic concern is to check the growth of Iran’s influence, remember that the fanatically Shia Iran and the fanatically Sunni Taliban are enemies. Iran is as eager to see the Taliban defeated as it was to welcome our overthrow of its enemy, the secular Sunni Saddam Hussein.

Next, it is an indisputable fact that indefinite involvement in Afghanistan, as well as Iraq, and a greater intervention in Syria call for a greatly increased military budget, which comes either at the expense of a much greater deficit.

I do not agree with the claim that Social Security and Medicare are destined to be cut back in the future because of the economic logic of these programs. They can, in fact, be sustained fairly easily by some policy changes that do not impinge on the ability of older people to live decent lives. But I do acknowledge that if the McCain-Graham-Ayotte faction in the Senate succeeds in significantly increasing the military commitments we are now making in the Middle East and extending them indefinitely, we will have trouble financing these programs.

To return to the headline I cited last week, we never owned Afghanistan, and we therefore cannot lose it.

I will be sorry from the standpoint of the Afghan people if the Taliban regains control. And we have the right to make it very clear that any repeat performance of Afghanistan being used as a base from which to attack Americans would bring severe retaliation, including the use of drones to kill people who would kill us. In extreme cases, should the Taliban allow itself to be used as a significant base for attacks on us or on our allies, we should make it clear that we will respond.

But that is very different than announcing that we will maintain a sufficient indefinite military presence to guarantee the victory of our side over the other side. The American military protects us. There will be times when we will have to ask them to extinguish a particular threat. But that in no way dictates that we should, at the cost of hundreds of billions over coming years, make sure that the civil wars in Syria, Iraq and Afghanistan are won by those we prefer.

I repeat, I understand why Obama fears being accused of “losing Afghanistan” and why Hillary Clinton has joined in supporting his decision in this regard. But I strongly believe they are underestimating the willingness of the American people to be realistic about what we cannot accomplish.

The hawkish critics of the president understand this. For all their denunciation of the president for being unwilling to sustain a major American fighting presence in those countries, they have never moved within Congress to authorize it. The reason is clear: They are aware that the voters, faced with this choice, would reject it.

The final point, which both the president and former Secretary Clinton should understand, is this: No reasonable step they take will blunt the criticism from the right. Those who think it is in America’s absolute interest to make sure the Taliban never defeats the Afghan government correctly note that a few thousand more soldiers of the sort the president is talking about for another year or two will not make a vital difference.

The critics are calling for a massive, expensive, indefinite commitment to make sure that those countries are governed well. We cannot afford this, we could not accomplish it if we wanted to and our strategic interests do not demand it.

Barney Frank is a retired congressman and the author of landmark legislation. He divides his time between Maine and Massachusetts.

Twitter: BarneyFrank