Bing West, a former Pentagon official who has done impressive ground-truth reporting on military action, urges in the Washington Post that the United States not send forward air controllers to work with Iraqi troops. He defends military leaders who recommend against deeper military involvement.
There's a political twist to his argument -- the President Obama is reluctant to support large scale military actions, and attendant casualties and consequences, so we shouldn't start up that escalator. I would counter that the President is wisely seeing the limits to U.S. military capabilities and the public opposition to another major war in the region. But I share West's view that Republican candidates should not pretend that halfway measures can achieve success.
As he says, "Republicans should not be advocating incremental escalation reminiscent of Vietnam."
To illustrate, the alleged Chinese hacking of US government personnel records, evidently in search of files on people who have held sensitive national-security jobs, was massive, sophisticated and possibly consequential; but it could not be, and was not, considered an act of war. This does not preclude some sort of US reprisal, perhaps a comparably bold robbery. (Presumably, the United States would not want China to know of such retaliation, lest it be foiled.) What is precluded in this case, by our way of thinking, is a US response so destructive or disruptive that it would cross the threshold from cyber espionage to cyber war – thus war. Admittedly, the line between intensely harmful theft and cyber war is woolier in reality than in theory. But the points stand that not all hacking is cyber war; that when it comes to espionage, states will be states; and that retaliation should be broadly in kind.