By MICHAEL SCHMIDT and ERIC SCHMITT
BAGHDAD — The Islamic State’s latest suicide attack in Baghdad, which killed nearly 330 people, foreshadows a long and bloody insurgency, according to American diplomats and commanders, as the group reverts to its guerrilla roots because its territory is shrinking in Iraq and Syria.
Already, officials say, many Islamic State fighters who lost battles in Falluja and Ramadi have blended back into the largely Sunni civilian populations there, and are biding their time to conduct future terrorist attacks. And with few signs that the beleaguered Iraqi prime minister, Haider al-Abadi, can effectively forge an inclusive partnership with Sunnis, many senior American officials warn that a military victory in the last urban stronghold of Mosul, which they hope will be achieved by the end of the year, will not be sufficient to stave off a lethal insurgency.
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