On Friday afternoon, President Trump will outline a new Iran policy.

We expect the president will say he cannot certify that the Iran nuclear agreement is in America's national security interest. Yet we also expect the president to do so carefully, explaining that his decision does not decertify the deal.

It looks like the first step in placing a more serious check on Iranian aggression in the Middle East.

Trump will be pilloried by the press, by Democrats wed to former President Barack Obama's Iran approach, and by overeager Iran hawks. But if Trump plays his hand as we expect, it will be a boon to world peace and to U.S. interests.

Flatly decertifying the Iran deal would be a mistake. Decertification would alienate America's European allies. Those allies will be very useful in applying pressure on Iran, and they are wedded to the deal. Germany and France, who have significant economic interests in Iran, would be particularly put off by decertification.

But by also refusing to certify the deal's harmony with U.S. interests, Trump sets the stage for improving the deal.

Trump can now push these U.S. allies towards a consensus on reforming the deal's inspections and nuclear and ballistic missile development protocols. As we noted last week, if European leaders are unwilling to cooperate, Trump can formally decertify the Iran deal in January, and ask Congress to sanction European multinational companies doing business with Iran.

It's straight from Trump's "art of the deal" philosophy: "Deal with me, or I'll deal alone."

If he scrapped the deal outright this week, Trump would be giving up leverage over both Europe and Iran.

On the flip side, Obama gave up all leverage by making it clear he would never walk away, no matter what. A counterparty who can't walk away will get the short end of the deal. Obama was desperate for an Iran deal at any cost, and so we've paid a very high cost, including a loss of influence across the Middle East. And American weakness has fueled conflicts such as that of Saudi Arabia and Iran in Yemen. But that's just the start of what American appeasement has wrought.

It has enabled unchecked Iranian influence in Lebanon; allowing Hezbollah, which holds 12 seats in the Lebanese parliament, to dominate a pro-American Future Movement party, which holds twice as many seats. Across Iraq, Iranian-led Shia militias have abused Sunni civilians and fueled the sectarianism that empowers the Islamic State. In Baghdad, Iranian blackmail has prevented the government of Haider al-Abadi from advancing its national reconciliation agenda. In Syria, Iran's alliance with Bashar Assad and Russia has taken hundreds of thousands of lives and portends a contiguous Iranian dominion from Tehran to Beirut. And an exigent threat to Israel.

Realism demands a rebalancing of power. In turn, Trump can now educate Iran's supreme leader, Ayatollah Ali Khamenei, and the Revolutionary Guards to a new American understanding. An understanding that prefers peace, but refuses to accept city streets as playgrounds for Iranian terrorism and plots against U.S. allies with a laissez-faire attitude.

Following the best tradition of America's Cold War strategy, Trump's strategy matches a realist conception of threat to the long-term pursuit of peace.