Al-Qaida is back.

Only three short years ago, the Islamic terror organization founded by Osama bin Laden was declared close to extinction by intelligence and diplomatic sources: its presence crushed in Iraq; bin Laden and his top lieutenants slain; and rival organizations riding the rising tide of the Mideast movement known as Arab Spring.

Less than two weeks ago, a New York Times report galvanized the notion of al-Qaida’s irrelevance, contending the Sept. 11, 2012 fatal attack on the U.S. consulate in Benghazi, Libya, did not involve any al Qaeda affiliates.

Now, it appears the reports of al-Qaida’s demise have been greatly exaggerated.

Last week, al-Qaida-linked forces reportedly took control of the city of Fallujah in west-central Iraq. Fierce clashes continued this week between Iraqi special forces and the al-Qaida-linked militants just west of Fallujah, a flare-up in a days-long standoff.

A decade ago during the second Gulf war, 107 U.S. and coalition forces died and another 613 were wounded in the battle to take Fallujah, the bloodiest battle of the entire war. The al- Qaida resurgence trivializes the coalition deaths and adds insult to their injuries.

The rise, fall and return of al-Qaida is significant in understanding how the militant group functions.

“Al-Qaida the organization(s) and al-Qaidism the idea are thriving across the Arab world like never before,” writes Brookings Institute representative Bruce Riedel for Al Monitor, a Mideast news website. Al-Qaida’s resurgence fills a vacuum left in “the failure of the Arab Awakening to create competent reformist governments,” Riedel continues, adding, “The counterrevolution keeping old autocrats in power or putting new ones into power is already creating the next generation of al-Qaida converts.”

Unfortunately, the return of al-Qaida also fills a vacuum left by the departure of U.S. troops in late 2011 — they’re not likely to return to Iraq anytime soon.

In a very large sense, the resistance never left Fallujah: its proponents — mostly members of former dictator Saddam Hussein’s minoriy Sunni sect — had simply stopped calling themselves al-Qaida.

Likewise in Benghazi, the resistance that killed four Americans, including the U.S. ambassador, may or may not have had official ties to al-Qaida, but to borrow former Secretary of State Hillary Clinton’s declaration: what difference does that make now?

But another element — the civil war in Syria — cannot be ignored. Turkish columnist Semih Idiz warns the al-Qaida rebels in Syria are intent on expanding their battle front into Iraq and other neighboring nations.

In light of the developments in Fallujah, now is not the time for the United States to abandon its interests in Iraq or lose sight of its long-term Middle East objectives.

The only appropriate response to al-Qaida is aggressive vigilance. The fight now belongs to Iraq, but Iraq will continue to require strong U.S. support, not only in intelligence and diplomacy, but in continued financial and military aid to Iraq’s fragile democracy.