Vali Nasr is dean of Johns Hopkins University's School of Advanced International Studies.

President Trump is set to roll out his Iran policy. The first step will be to "decertify" the Iran nuclear deal, which will then set the stage for a broader campaign of economic and military pressure meant to weaken and contain Iran. This risky gambit will undermine U.S. credibility and the international community's ability to manage further nuclear developments in Iran, North Korea and other places down the line for years. The blowback to U.S. national interests, however, goes much further.

Why do it? It seems clear that Trump disdains the Iran nuclear deal, at least in part, because it is a signature accomplishment of the Obama presidency — a legacy perhaps second only to the Affordable Care Act in its symbolic significance. That helps explain why the president has described the deal as an "embarrassment" and "the worst deal ever," hyperbole that has only made it more difficult for him to regularly report to Congress that Iran is actually doing its part.

The president prefers to wash his hands of the deal and let Congress decide its fate. Refusing to confirm Iran's compliance while laying out a broad case against Iran will, in effect, invite Congress to impose new sanctions. But if other signatories to the deal side with Iran in declaring the United States in violation and resist U.S. pressure to curtail their business dealings with Iran, all that "decertification" will achieve will be to open a rift between the United States and its European allies, Russia and China. On the other hand, if the United States wins over its allies, the deal will be dead — and everyone can go back to worrying about war with a nuclear-armed Iran.

The United States is right to worry about Iran's missile program, as well as the scope of Iran's regional influence and the manner in which it asserts that influence. But the course Trump is embarking on will only plunge an already volatile Middle East into greater turmoil, which will consume U.S. attention and resources.

Iranian leaders interpret Trump's hostility to the nuclear deal as proof that diplomatic engagement with the United States is a fool's errand — that Washington will not abide by any diplomatic agreement and will construe willingness to pursue diplomacy as weakness and an invitation to apply more pressure. Already, the commander of the Revolutionary Guard Corps has warned that Iran would retaliate against new sanctions, in particular the designation of the corps as a terrorist organization, by building and testing more missiles and labeling in kind the U.S. military a terrorist organization — then targeting U.S. bases and personnel.

Iran is not looking for war with the United States. But it is starting to think that it is better to act like North Korea. A recalcitrant, let alone aggressively anti-American, Iran would dramatically change the lay of the land for U.S. foreign policy in the region.

The nuclear deal removed the threat of war with Iran. That was an important strategic win given Iran's size, location and importance to stability in a vast region stretching from Central Asia to the Mediterranean. There were other benefits. The deal made it possible for Iran and the United States to tacitly cooperate in the fight to roll back the Islamic State's gains in Iraq. At stake in Trump's new Iran policy will be the stability of the central government in Iraq and its ability to arrive at a political understanding with the country's Sunnis and its restless autonomous Kurdish region. It is difficult to see how the crisis generated by the Kurdish referendum for independence could be defused without Iran. It is likewise difficult to envision a quick end to wars in Syria and Afghanistan if those countries become the theater for protracted U.S.-Iranian confrontation.

In Iran itself, the nuclear deal has been the calling card of moderate voices who wish to reform its economy and anchor the country's future in better relations with the West. Their success in negotiating the deal has created a constituency for change in Iran.

That constituency gave President Hassan Rouhani a resounding victory and a clear mandate in the presidential election in May. Rouhani ran a campaign built on the success of the nuclear deal and the promise of the opening to the West. In August, an overwhelming majority in the Iranian parliament — cutting across reformist and conservative party lines — voted to reconfirm Foreign Minister Mohammad Javad Zarif, the chief negotiator of the nuclear deal on the Iranian side. The deal has increasingly redrawn political battle lines in Iran along whether to invest the country's future in engagement with the United States.

There are those in the United States who would welcome the demise of the Iranian moderates; hard-liners at the helm in Tehran would make it easier to array U.S. forces against that country. But America learned in Iraq that it cannot bring change through the turret of a tank.

The United States will be better off if it is Iranians who bring about change in Iran. Yet Washington is falling victim to the same flawed logic that paved the way to the Iraq War. Trump's Iran policy is not just an attack on President Barack Obama's foreign policy legacy; it will also define his own. History will not be kind to this strategic blunder.