For decades, we have been hearing that the people of Iran despise their authoritarian radical Islamic regime. They reject the oppression as well as the mullahs’ determination to take the once-modern nation backwards to the dark ages of fundamentalist rule.

Still, for more than 30 years, the Iranian people did little to show their discontent. Now, popular anger over domestic tyranny has merged with frustration over Iran’s interference in the domestic affairs of other countries throughout the region to provoke the most serious threat to the genocidal regime since the 1979 revolution.

For all the dissatisfaction in the past, the public did not revolt, because they seemed unprepared to fight for independence against the overwhelming force of the brutal Revolutionary Guards. The one time the public did rise up, in 2009, they were ruthlessly suppressed by the guards and abandoned by the international community, most notably by Barack Obama. The former president betrayed not only the Iranian people by his failure to support the uprising, but also betrayed the rest of the world, which has faced an increasingly aggressive Iran ever since.

We have subsequently learned that Obama’s desperation to sign a nuclear agreement to have something to show for his otherwise inconsequential foreign policy legacy led him to agree to a nuclear deal so flawed that Iran has continued to advance toward regional dominance and a nuclear weapons capability.

Most recently, it was revealed that Obama went so far as to sabotage his own administration’s efforts to bring Iran’s Hezbollah terrorist arm to justice for its drug-trafficking crimes for fear that would interfere with negotiations with Iran on the nuclear deal and undermine Obama’s propaganda line that the agreement would lead Iran to stop threatening U.S. interests. Obama also did nothing to address Hezbollah’s global terrorist activities.

By refusing to certify the Iranian nuclear agreement, President Trump has taken an important first step toward reversing the catastrophic impact of Obama’s Iran policies. Now he has an unexpected opportunity to support the one policy that could end the Iranian threat to its neighbors, to the United States and to the world: namely, regime change. That is the only way to stop the genocidal and hegemonic ambitions of the Iranian government.

Obama’s unwillingness to punish Iran for their continued violation of UN resolutions related to their nuclear activity and ballistic missile development emboldened the mullahs, who subsequently expanded their missile program, continued their covert nuclear weapons pursuit, increased their sponsorship of terror, and intensified their interference in their neighbors’ affairs. Thanks to the billions of dollars Obama paid Iran in ransom, and the billions more in sanctions relief afforded by the nuclear deal, Iran grew stronger and its tentacles now extend throughout the Gulf, into Yemen, Syria, Lebanon, Gaza and beyond.

Trump now has the opportunity to work for regime change without necessarily using military force. He can provide verbal and, more important, material support to the protestors. He can increase sanctions against Iran for brutalizing their people if the Iranians use the Revolutionary Guards to try to suppress the demonstrations.

For example, Iran should be cut off from the international banking system. That could cripple the economy and prevent the Europeans from continuing their mad rush to sign business deals with the Iranian government. Oil should also be embargoed. The sale of Boeing jets to Iran must be cancelled. The cases against Hezbollah’s illegal operations in the United States must be reopened and warrants sought for those responsible for attacks against Americans abroad. Furthermore, U.S. forces in Syria and Iraq, which succeeded in destroying ISIS, should now be directed to drive out Iranian and Hezbollah fighters.

Even the feckless Europeans would be unable to complain about tightening sanctions without looking like they are supporting the dictators in Tehran over the people in the streets clamoring for democracy. Perhaps Russia and China would again shield Iran at the UN Security Council with their vetoes, but the United States does not need the UN’s permission to help the people of Iran free themselves from the grip of the extremists who have turned Iran into one of the world’s greatest violators of human rights and threats to global peace and security.

The president must pledge whatever support the protestors need to bring about the end of the reign of terror of the mullahs. They should be given the assurance that sanctions will cease and aid will flow to a new government that adopts democratic principles, forswears its nuclear weapons program, ends ballistic missile research, ceases sponsorship of terror, stops its genocidal threats against Israel, and ends its interference in the affairs of its neighbors.

We are at a historic moment when one of the world’s most evil regimes can be destroyed. Obama let the moment pass in 2009 with devastating consequences. President Trump and other world leaders cannot afford to make the same mistake.

Rabbi Shmuley Boteach, “America’s Rabbi,” whom The Washington Post and Newsweek call “the most famous Rabbi in America,” is the international bestselling author of 30 books, including his most recent, “The Israel Warrior.” Follow him on Twitter @RabbiShmuley.