Don’t just rely on Benjamin Netanyahu’s passionate advice to Congress on his way to reelection that Iran is our arch enemy. Now we have the counsel of retired general David Petraeus, who gave a remarkable interview this week to the Washington Post. General Petraeus agrees with Mr. Netanyahu: Iran, not the Islamic State, is the real enemy.

The general’s message: “I would argue that the foremost threat to Iraq’s long-term stability and the broader regional equilibrium is not the Islamic State; rather, it is Shiite militias, many backed by — and some guided by — Iran.” The general adds, “Longer-term, Iranian-backed Shia militia could emerge as the preeminent power in the country, one that is outside the control of the government and instead answerable to Tehran.” (Italics mine.)

Mr. Netanyahu is arguing against a bad United States-Iran deal that might end the economic sanctions and permit Iranian nuclear development after ten years. (Of course, nobody believes Iran will wait for, or permit, true verification.) But the thrust of the Petraeus interview is that unless American military strategy completely changes, Iran is going to take over Iraq.

General Petraeus gives ample evidence of this: These Shiite militias are being run by Iran’s top military man, General Qasem Soleimani. He’s the head of the Quds Force of the Revolutionary Guard. He has been spotted and filmed on the ground in Iraq. And he has been making battlefield tours the way General Petraeus did during the surge.

In the Post interview, General Petraeus relates a remarkable story: In the midst of the surge, the general got a note from Soleimani: “General Petraeus, you should be aware that I, Qasem Soleimani, control Iran’s policy for Iraq, Syria, Lebanon, Gaza, and Afghanistan.” (Italics mine.) General Petraeus told the intermediary he could tell Soleimani to “pound sand.”

Overall, General Petraeus makes it clear that the current Iranian regime “is not our ally in the Middle East,” is part of the problem, not the solution, and is “deeply hostile to us and our friends.” Though General Petraeus never mentioned President Obama’s name, it’s clear that the general is splitting from administration policy.

And isn’t all this what Bibi Netanyahu told the U.S. Congress? Didn’t he say Iran’s goal is to control the whole area, and of course attempt at some point to blast Israel off the face of the Earth?

So why are Mr. Obama and Secretary of State Kerry trying to do business with Iran? If we know who the militias really are and know that Iran wants to take over Iraq and control the whole region, why is the United States talking about lifting economic sanctions and negotiating some sort of accommodationist deal with our arch enemy?

And why is the U.S. doing this with oil down 50% and Iran a high-cost producer? The economic table is set for a catastrophic fiscal blow to Iran — our enemy.

According to a Wall Street Journal news report, Iran needs $130.70 a barrel of oil to balance its budget. The price of Brent crude is about $55, or roughly 60% below what Iran needs. It’s hard to get credible economic numbers for Iran, but it’s a safe guess that the budget is most of the state-run economy. Therefore, cheap oil is deadly for Iran.

So I ask again: Why are we helping them? We’ve got Iran on the ropes. Why loosen the sanctions?

Talking to the Post, General Petraeus acknowledges that we moved troops out of Iraq way too soon and in doing so sent a signal of weakness that we were pulling back from the Middle East overall. I would guess that these last-ditch efforts at an Iranian treaty will be perceived as even greater U.S. weakness in the Middle East.

Who knows if this can be stopped? Surely the Senate must vote on any U.S.-Iran deal. But the conundrum is, if we know Iran is our enemy, if we know Iran wants to conquer the Middle East, if we know Iran wants to destroy Israel, if we know Iran is continuing to develop nuclear weapons, and if we’re hearing all this not just from the Israeli prime minister, who has the burden of defending his nation, but also from a retired general who is out of office and has no skin in the game, why won’t the present administration come to acknowledge the real situation, reverse course, and halt any efforts to placate our arch enemy Iran?

Why do we even have to ask this question?