Al-Qaeda in Iraq (AQI), which has staged a bloody comeback in Iraq in recent months, issued a threat this week to strike at the “heart” of America.

On Sunday, shortly before a string of AQI attacks killed more than 100 people, AQI leader Abu Bakr Baghdadi warned Americans: “You will soon witness how attacks will resound in the heart of your land, because our war with you has now started.”

Testifying before the House Homeland Security Committee yesterday, Mathew Olson, the director of the National Counterterrorism Center, assessed the potential threat posed to the United States by AQI and noted that several associates of the terrorist group had been arrested inside the U.S. and Canada in the last two years.

Although al-Qaeda was caught off guard by the “Arab Spring” uprisings in many countries, its regional franchises have exploited the resulting chaos and power vacuums, particularly in Yemen, Libya and Syria. Al-Qaeda leader Ayman al-Zawahiri has urged his followers to expand their operations in Syria, and an influx of Islamist militants there has heightened concerns about Syria’s massive chemical weapons stockpile.

AQI had been severely degraded by U.S. and Iraqi security forces in an intensive counter-terrorism campaign from 2006 to 2011. But the resilient terrorist organization has revived and thrived after the withdrawal of U.S. troops in December 2011. Heritage Foundation analysts warned repeatedly that one of the negative impacts of the abrupt U.S. military withdrawal from Iraq would be a slackening of counter-terrorism efforts against AQI.

Iraqi Prime Minister Nouri al-Maliki quickly moved against his Sunni rivals to consolidate his power after the withdrawal of U.S. troops. This aggressive political purge has further alienated Iraqi Sunni Muslims who had previously turned against AQI.

Now AQI is opportunistically exploiting Sunni–Shia tensions in Iraq and intensifying Sunni–Alawite tensions in Syria. Although its primary victims are likely to continue to be Iraqis and Syrians, it could soon pose a significant threat to the U.S. homeland as well.