According to this Reuters dispatch, the FBI has warned of a threat by ISIS to blow up the Memphis & Arkansas Bridge, connecting Memphis, Tennessee and West Memphis, Arkansas.

The Federal Bureau of Investigation passed the threat on to local police in a bulletin out of an "abundance of caution," spokesman Chris Allen said.

"This is an unsubstantiated, anonymous threat," he said, adding that there was no useful intelligence arising from it.

It is probably just bluster, but it does indicate that American homeland targets are aspired to by ISIS, and that they will not necessarily be high profile New York or Washington structures. In fact, choosing heartland targets would, if successfully attacked, be far more effective in accomplishing the aim of striking terror into the American mind.