As the world and the U.S. Congress examine the Iran deal's fine print, the strategic large print is clear enough. "Obama wants this [deal] as a centerpiece of his legacy," an anonymous American diplomat is quoted as saying, "and he believes a peaceful Iran could be a bulwark against ISIS in the Middle East and the key to peace there."

The determination to engage enemies is a hallmark of Obama's foreign policy. With Iran, as with Cuba, he hopes to upend old strategies of isolation and sanctions, drawing rivals into a web of cooperation that ends up improving their behavior. It is Obama's version of regime change — the nonviolent advance of rational, modern norms because they are, well, rational, modern norms.

So the Iran deal is really a high-stakes, strategic bet. The agreement allows a decade of managed and monitored nuclear proliferation while Iran is engaged, first on security, but eventually across the range of the relationship. Under the terms of the agreement, Iran will emerge from this period as a nuclear threshold state, free from most sanctions, but hopefully, by that point, a "key to peace." The alternative, the president argues, is a path of isolation and confrontation that is likely to lead to war.

But is Obama's bet a reasonable one? Is he playing blackjack or the lottery?

In an interview with Ruth Marcus and me for the Washington Post Campaign Close-up series, Sen. Lindsey Graham describes Obama's approach to Iran as "dangerously naive." "I think he's misjudging what the Iranians want," Graham argued. "And the best evidence of what they want is what they're doing right now to destabilize the region without nuclear weapons."

There is no evidence that Ayatollah Ali Khamenei is a Gorbachev-like figure. Iran gives every indication of being an aggressive, revolutionary power. It is rallying, arming and directing military forces in Lebanon, Yemen, Syria and Iraq. The reported agreement to partly lift the arms embargo against Iran — a dramatic concession — must seem to America's Sunni allies and partners like de facto U.S. recognition of Iranian spheres of military influence across the region. Because it is.

Syria is a good example of the side effects of Obama's bet. During four years of civil war, America has hardly been a factor. This has resulted, in part, from habits of indecision that have added up to a policy of nonintervention. But American strategy in Syria has also shown increasing deference to Iran — and thus Iran's proxy, the Bashar Assad regime — in order to avoid confrontations that might disrupt nuclear negotiations.

The shift has been remarkable. Obama has gone from demanding in 2011 that Assad "step aside" to downplaying, earlier this year, the Syrian ruler's use of chlorine gas, since it has "historically not been listed as a chemical weapon." The fragile nuclear talks could not be jostled, at apparently any cost.

For years, the Sunni powers called for more aggressive American leadership in Syria. But American support for its proxies, such as the Free Syrian Army, proved minimal and unreliable, pushing many recruits toward better-armed, more radical alternatives. Now Turkey, Qatar and Saudi Arabia have given up on an American-led response, throwing their support behind a Sunni rebel alliance that includes the Nusra Front, a local Al-Qaida affiliate.

Assad, after a series of military reverses, leads a battered and diminished army, only sustained by Iranian cash and supplies. His collapse — now a distinct possibility — might set off a race for Damascus between Al-Qaida and the Islamic State. And the U.S. — having betrayed its proxies and alienated its allies — would merely be a bystander as a terrorist flag is raised over the capital of a ruined and wretched country.

This bystander status looks like America's future in much of the Middle East. The economic payout of the nuclear deal will fund Iranian military activities across the region. And haggling over implementation will continue indefinitely. Just as Obama has been loath to throw away the possibility of a deal by getting tough with Iran, he will be loath to throw away the reality of a deal by getting tough with Iran. And the economic pressure that has influenced Iranian behavior in the past will be gone, with no realistic hope for a "snap back" of sanctions.

The deal amounts to the gradual passing of a leadership baton to one of the worst regimes in the world, on the hope its nature will change. Obama has bet the future of the Middle East, and America's influence in the region, on a play of the lottery.

Michael Gerson's column is distributed by the Washington Post Writers Group. He's at michaelgerson@washpost.com.