Sanctions and isolation have weakened Iran but it is still in a strong position to expand its influence in the Middle East.

Iran may not be the Middle East’s hegemon today and its nuclear deal with world powers — which would lift sanctions in return for curbing its atomic program — may not make it much easier for the Islamic republic to attain such a status. But someone needs to tell the Iranians.

The libertarian Cato Institute’s Justin Logan makes a convincing case for why fears of Iranian hegemony are overblown.

Even before international sanctions took full effect, its economy comprised only about 11 percent of the Middle East’s total gross domestic product, he points out — against 22 percent for its main Sunni rival, Saudi Arabia.

“Iran’s share of the region’s military expenditures is similarly unimpressive at 9 percent.” Saudi Arabia, by contrast, accounts for almost 45 percent of the Middle East’s defense spending.

Iran’s military is also outdated, forcing it to rely on terrorist proxies, like Hezbollah in Lebanon, to project power outside its borders.

Logan is right to argue that Iran’s influence over other allies is often overstated.

Political tumult in the region has opened the door to Iranian meddling in places like Yemen but Tehran holds much less influence than is often argued and it no more “controls five capitals” than does the United States. Iran has little control over these volatile theaters and Tehran’s proxies buck Iran frequently.

The Houthis in Yemen may be Shia like Iran but Saudi claims of Iranian influence there are exaggerated. Iran did not engineer the Houthi uprising nor has it given the group significant support, even after it took over the capital, Sana’a, in February.

Similarly, Shia insurgents and politicians in Iraq are backed by Iran but not controlled by it.

Where Logan might be too sanguine, however, is in his dismissal of Iran becoming more powerful.

He argues that “even to suggest that Iran has a shot at dominating the region defies both history and logic.” Yet it has dominated the Middle East in the past and logic suggests it is in a stronger position than any other power in the region.

Robert D. Kaplan and Kamran Bokhari have argued that whereas Saudi Arabia is “built around the parched and deeply conservative upland of Najd which has always struggled to subdue the more cosmopolitan maritime peripheries like Hijaz,” Iran is a coherent geographical entity that “straddles the Middle East and Central Asia as well as the two energy producing regions of the Persian Gulf and the Caspian Sea.”

Rather than an artificial contrivance of a single family, Shiite Iran — with its relative geographic logic — is heir to Iranian states going back to antiquity, when Persia was the world’s first superpower. Iran encapsulates a rich and eclectic civilization. Even under the present regime, in Iran there is a semblance of a democratic foundation, while in Saudi Arabia there is an utter lack of any sense of democracy.

Regardless of whether the nuclear deal with Iran will strengthen the regime or foreshadow its downfall; regardless of Iran’s intentions, it has the capacity to become if not the region’s hegemon then certainly something close to it.

And Iran’s leaders know it.

In testimony to the United States Senate on Wednesday about the nuclear agreement, The American Interest ‘s Walter Russell Mead argued that Iran “is the one country at the moment that appears to believe that it has both the capacity and the will to establish a hegemonic position in the region.”

If it succeeds, he warned, that would threaten the United States’ interest in a peaceful Middle East where no single power dominates and oil can flow freely from to economies in Asia and Europe.

But even if it fails, Iran’s mere attempt “could create such chaos and upheaval in the region that normal governance would break down and some oil-exporting countries could be paralyzed by international or civil conflict.”

Mead’s colleague, Adam Garfinkle, similarly argued last year that Iran’s hegemonic exertions had already “raised an existential threat to the Sunni Arab regimes” of the Middle East and “radicalized heretofore mostly latent sectarian cleavages in the region” — most notably the self-declared Islamic State, or ISIS.

When the feeble Sunni Arab states proved feckless in responding, the radicalization process, with mischievous help from countries like Qatar as well as Turkey, created the monster that is ISIS. The point? It is not possible to extirpate ISIS unless we also address its source: Iranian power projection through Arab Shia militias (which, by the way, extends all the way to the Houtis in Yemen).

The point is that Iran doesn’t have to become a hegemon to set off a regional conflagration. It already has because its rivals are acting to prevent an Iranian hegemony — because, rightly or wrongly, they believe it’s a possibility.

World powers’ nuclear agreement with Iran, Mead warned on Friday, could strengthen Iran in this dynamic. It unfreezes Iranian assets overseas, allowing it to ramp up support for proxies like Hezbollah and Bashar al-Assad in Syria, whom the Sunni powers are determined to defeat. The resumption of normal trade relations should make Iran richer over the long term. And the lifting of an arms embargo could see Iran modernize its armed forces with help from Russia.

These worries loom larger because Iran, under sanctions and suffering serious economic privation, has nevertheless been able to operate effectively in regional politics, scoring gains against Sunni adversaries that have seriously alarmed some of its neighbors. If an isolated and economically challenged Iran could achieve such results, one must ask what it can achieve under the more favorable conditions that will follow the implementation of the [nuclear agreement].