Even the Iran deal’s most ardent supporters are beginning to suspect it won’t mellow the mullahs. Alas, that’s not the worst of it — because the deal is actually boosting Iran’s darkest forces.

According to a study to be released Tuesday by the Washington-based Foundation for Defense of Democracies, Iran’s Revolutionary Guards — and not ordinary Iranians or the country’s much-vaunted “moderate” cleric-politicians — are the ones who’ll gain the most from the Joint Comprehensive Plan of Action, the deal the mullahs signed with six world powers one summer ago.

“As the 2015 nuclear deal is implemented, it is the [Guard Corps] that is poised to benefit most,” concludes the 48-page, painstakingly detailed study by four FDD researchers.

Titled “How the Nuclear Deal Enriches Iran’s Revolutionary Guard Corps,” the study surmises that the IRGC controls as much as 40 percent of the country’s economy, including sectors related in one way or another to the very nuclear program the deal is meant to curb.

Look out: Your tax dollars were recently transferred to Iran by the Obama administration. And much of that dough will make the Iranians who wish “death to America” very, very rich.

The cash will also help them tighten their hold on power at the expense of politicians who think engagement with us is the way to save the Khomeini revolution.

The IRGC was established in 1979 by Ayatollah Khomeini as a militia to spread the revolution’s ideology and consolidate its hold on power. It eventually grew into a formidable army that operates in parallel to the Iranian military.

The corps’ al Quds unit has been zealous exporting the revolutionary ideology around the globe, one way or another. It’s now active in such theaters of war as Yemen, Lebanon and Syria, where it abets President Bashar al-Assad’s bloodbath and is the main reason he’s still in power.

In the Persian Gulf, IRGC boats often buzz US Navy vessels. In January, the corps kidnapped 10 American sailors who accidentally strayed into Iranian waters. Several incidents since then have nearly led to direct confrontation between America and Iran.

Another IRGC arm, the Basij, is charged with enforcement at home. Women (including participants in this week’s world chess championship there) must be “properly” covered. Elections must have the “proper” results; in 2009, the Basij forcefully suppressed a popular uprising and beat to submission those who were angry over a stolen presidential election.

As the FDD study documents, the corps also has extended its tentacles through every corner of the economy. Khomeini’s heir, the current supreme leader Ayatollah Khamenei, is mostly responsible for the IRGC’s financial growth.

In 2005, Khamenei issued a decree that would seem on its face to be a reformist’s dream: 25 percent of the economy was to be transferred to the private sector within five years. But there was a catch: According to the FDD study, a “significant portion” of the transfer would go to the IRGC, rather than the private sector. By now, the Guards control much that matters in Iran.

The Treasury Department has sanctioned 25 companies, 25 individuals and two academic institutions for being controlled by the IRGC. Yet the FDD researchers identified at least 229 companies over which the IRGC has “significant influence.”

True, the nuclear deal did leave some sanctions over the IRGC intact, at least for the time being. But many of those will expire in the coming stages of the deal. Meanwhile, the IRGC is raking it in from the easing of other sanctions.

And though the group is behind extensive global terrorist activity — including a foiled plot to assassinate the Saudi ambassador with a bomb in the heart of Washington, DC — the State Department has yet to designate the IRGC, or even its external arm, the al Quds force, as a foreign terrorist organization.

The FDD study recommends Washington take that step — along with several others to beef up sanctions and other levers that will increase pressure on Iran’s most dangerous organization.

As one of the study’s authors, Emanuele Ottolenghi, tells me, “The Guard’s growing economic clout is an end in itself and a tool to support its nefarious activities throughout the region.”

“Negotiate with Iran, fight the Guards” was the course that a Reagan administration veteran, Abraham Sofaer, advised just before the Iran deal was signed. In his legacy-setting diplomatic achievement, President Obama instead strengthened the Guards.

The study urges the next president and Congress to change that course and to force foreign investors to realize there’s a huge risk of doing business with Iran’s worst of the worst.

Question is: Will Hillary Clinton or Donald Trump listen?