The Next Target of ISIS: Western Nations?

In the wake of two US airstrikes against ISIS, supporters of the extremist group that's been seizing towns in northern Iraq are calling for retaliatory strikes against America, CNN reports. "It is a clear message that the war is against Islam and the mujahideen," wrote the administrator of an online ISIS forum. "The mujahideen must strive and seek to execute proactive operations ... to discipline America and its criminal soldiers." Other ISIS followers are deriding the US with the Twitter campaign #AmessagefromISIStoUS and posting photos of the 9/11 attacks (which isn't really new—they used the Twitter handle #CalamityWillBefallUS after ISIS took Mosul in June). Possible ways ISIS might strike the West include:

• A "crash" program: In this scenario, ISIS spends some of its tens of millions of dollars on arming European extremists who have joined the group (officials estimate there are up to 1,000 of them). This could reach American soil, because many Europeans can enter the US without a visa, and there's talk of sophisticated bombing devices that can slip past airport security.
• Returned fighters: Extremists who fought for ISIS in Syria and returned home "could take matters into their own hands," says CNN. Case in point: Mehdi Nemmouche, the French-Algerian accused of killing four people at a Jewish museum in Belgium this spring.
• "Lone wolves": The Boston Marathon bombing—enough said.

Meanwhile, the effects of US military strikes aren't entirely clear, but the New York Times reports that almost two dozen ISIS fighters were killed and at least 30 injured near Mosul, and al Jazeera says the airstrikes have allowed Kurdish forces to reach Yazidi refugees on Sinjar Mountain and save more than than 5,000 of them. (See why President Obama says the Iraq intervention will be "long term.")