Former U.S. Ambassador to the United Nations John Bolton said America, post-September 11 terror attacks, has failed to put into practice lessons that should have been learned — lessons about the truths of radical Islam, terror and national security.

In a piece for the Gatestone Institute, Bolton said radical Islamism has hardly faded and disappeared from the world stage.

In fact — it’s grown and spread, due in large part to the West’s utter failure to recognize truths, admit them and act accordingly.

Here’s what he wrote, in Gatestone:

Today marks the 16th anniversary of al-Qaida’s 9/11 attacks. We learned much that tragic day, at enormous human and material cost. Perilously, however, America has already forgotten many of Sept. 11’s lessons.

The radical Islamicist ideology manifested that day has neither receded nor “moderated” as many naive Westerners predicted. Neither has the ideology’s hatred for America or its inclination to conduct terrorist attacks. Iran’s 1979 Islamic Revolution brought radical Islam to the contemporary world’s attention, and it is no less malevolent today than when it seized our Tehran embassy, holding U.S. diplomats hostage for 444 days.

The Taliban, which provided al-Qaida sanctuary to prepare the 9/11 attacks, threaten to retake control in Afghanistan. Al-Qaida persists and may even be growing worldwide.

While ISIS’s caliphate in Syria and Iraq will not survive much longer, countries across North Africa and the Middle East (“MENA”) have destabilized or fractured entirely. Syria and Iraq have ceased to exist functionally, and Libya, Somalia and Yemen have descended into chaos. Pakistan, an unstable nuclear-weapons state, could fall to radicals under many easily predictable scenarios.

The terrorist threat is compounded by nuclear proliferation. Pakistan has scores of nuclear weapons, and Iran’s program continues unhindered. North Korea has now conducted its sixth, and likely thermonuclear, nuclear test, and its ballistic missiles are near to being able to hit targets across the continental United States. Pyongyang leads the rogue’s gallery of would-be nuclear powers, and is perfectly capable of selling its technologies and weapons to anyone with hard currency.

During Barack Obama’s presidency, he ignored these growing threats and disparaged those who warned against them. His legacy is terrorist attacks throughout Europe and America, and a blindness to the threat that encouraged Europe to accept a huge influx of economic migrants from the MENA region, whose numbers included potentially thousands of already-committed terrorists.

Obama also ignored North Korea, affording it one of an aspiring proliferator’s most precious assets: time. Time is what a would-be nuclear state needs to master the complex scientific and technological problems it must overcome to create nuclear weapons.

And, in a dangerous unforced error that could be considered perfidious if it weren’t so foolish, Obama entered the 2015 Vienna nuclear and missile deal that has legitimized Tehran’s terrorist government, released well over a hundred billion dollars of frozen assets, and dissolved international economic sanctions. Iran has responded by extending its presence in the Middle East as ISIS had receded, to the point where it now has tens of thousands of troops in Syria and is building missile factories there and in Lebanon.

Before 2009, publishers would have immediately dismissed novelists who brought them such a plainly unrealistic plot. Today, however, it qualifies as history, not fantasy. This is the agonizing legacy the Trump administration inherited, compounded by widespread feelings among the American people that we have once again sacrificed American lives and treasure overseas for precious little in return.

These feelings are understandable, but it would be dangerous to succumb to them. We didn’t ask for the responsibility of stopping nuclear proliferation or terrorism, but we are nonetheless ultimately the most at risk from both these threats.

And as we knew during the Cold War, but seem to have forgotten since it ended, our surrounding oceans do not insulate us from the risk of long-distance nuclear attacks. We face the choice of fighting the terrorists on our borders or inside America itself, or fighting them where they seek to plot our demise, in the barren mountains of Afghanistan, in the MENA deserts, and elsewhere.

Nor can we shelter behind a robust national missile-defense capability, hoping simply to shoot down missiles from the likes of North Korea and Iran before they hit their targets. We do not have a robust national missile defense capability, thanks yet again to Barack Obama’s drastic budget cuts.

President Trump appreciates that nuclear proliferation and radical Islamic terrorism are existential threats for the United States and its allies. During the 2016 campaign, he repeatedly stressed his view that others should play a larger role in defeating these dangerous forces, bearing their fair share of the burden. But candidate Trump also unambiguously (and entirely correctly) called for restoring our depleted military capabilities because he saw that American safety depended fundamentally on American strength.

Sept. 11 should be more than just a few moments of silence to remember the Twin Towers falling, the burning Pentagon and the inspiring heroism of regular Americans in bringing down United Flight 93 in Shanksville, Pa. We should also seriously consider today’s global threats. Those who made America an exceptional country did so by confronting reality and overcoming it, not by ignoring it.