The greatest threat to national security today isn’t ISIS, or China, or Russia or even the administration’s favorite bogey, climate change. The greatest threat is the Islamic Republic of Iran, a regime that has been on a war footing toward the United States since 1979, mandates chants of “Death to America” in every mosque in the country at Friday prayers, and now, thanks to President Obama and John Kerry, is on the fast track to obtaining nuclear weapons.

Iran is not as flashy as ISIS but is actively working now on numerous anti-American initiatives that could turn out to be even more lethal than anything ISIS has yet perpetrated. In June 2011 Iran’s Supreme Leader, the Ayatollah Ali Khamenei, declared: “Wherever a movement is Islamic, populist and anti-American, we support it.”

In 2012, Khamenei called for terror attacks in the West — but now, because of Obama, Iran is newly flush with billions of dollars in sanctions relief to finance such attacks.

As I show in my new book “The Complete Infidel’s Guide to Iran,” the nation is a breeding ground for terrorist activity: funding and controlling a global network of jihad terror organizations with a truly global reach, ready to do Iran’s bidding up to and including the killing of its perceived enemies.

Chief in this network is Hezbollah, a wholly owned and operated subsidiary of Iran’s Islamic Revolutionary Guards Corps. Most notoriously, Hezbollah was responsible for the murder of 241 US servicemen in the bombing of military barracks in Beirut in 1983.

Iran has also been implicated in the bankrolling of the 1996 bombing of the Khobar Towers in Saudi Arabia, which housed members of the US Air Force, and in the 1998 bombings of the US embassies in Kenya and Tanzania, in which over 200 people were killed.

Iran’s Hezbollah doesn’t just operate in Lebanon. It continues to target the United States through Mexico, where it has teamed with drug cartels along the US border. This partnership is mutually beneficial: Hezbollah gets massive amounts of cash to finance its jihad operations, and the drug cartels receive extensive training in ways to strike terror into the hearts of their enemies. That is one principal reason why the Mexican drug cartels have adopted what up until recently had been two trademarks of jihad groups: kidnapping and beheading.

It’s not just Hezbollah that Iran bankrolls. Despite the Sunni/Shiite divide, the Sunni jihad groups Hamas and Palestinian Islamic Jihad, as well as the Shiite Houthis in Yemen and the Iraqi Shiite group Kata’ib Hezbollah are all funded by the Islamic Republic.

Nor does it work only through jihad terror groups: It has funded the Spanish left-wing populist party, Podemos — a vivid illustration of how the international left and the global jihad movement can and do make common cause against the West.

Iran was even involved in planning the 9/11 terror attacks: in the months leading up to the attacks, at least eight of the hijackers traveled repeatedly to Iran and met with Iranian agents there, who facilitated their travel to Afghanistan for training.

Iran is a breeding ground for terrorist activity: funding and controlling a global network of jihad terror organizations with a truly global reach.

Their passports were left unstamped by Iranian border guards so that they would be able to enter the United States undetected.

Iranian adventurism has continued. In 2012, the government of Canada closed Iran’s embassy in Ottawa and recalled its own diplomats from Tehran in protest of subversive activities by Iranians in Canada, directed from the Embassy.

Former Iranian diplomat Abolfazl Eslami admitted that Iran had been plotting subversive activities through their embassies in Canada and other countries. And earlier this year, the US indicted seven Iranian hackers linked to the government of the Islamic Republic for cyber attacks on US banks and a dam in New York state.

As a result of Obama’s supine appeasement policy toward the Islamic Republic, Iran is bolder and more belligerent than ever — as evidenced by its capture and public humiliation of US Navy sailors last January.

But it is not too late. While a new president will not be able to recover the money that Obama has showered upon Iran, the next chief executive can and should repudiate the nuclear deal and put the Iranian regime on notice that not only its pursuit of nuclear weapons, but its global adventurism will no longer be tolerated.

The Iranian opposition, however imperfect, that Obama refused to support in 2009 must be given active aid of all possible kinds. And any future negotiations with the Islamic Republic of Iran should only be entered into with a clear-eyed understanding of that regime’s bloodthirstiness, willingness to deceive and unshakable hostility to the United States.

Iran is more dangerous than ISIS, but the Iranian people are the heirs of one of the oldest civilizations on earth.

They deserve better than the Islamic Republic. As do we all.

Robert Spencer is the director of Jihad Watch and author of the New York Times best-sellers “The Politically Incorrect Guide to Islam (and the Crusades)” and “The Truth About Muhammad.” His latest book is “The Complete Infidel’s Guide to Iran.”