It might be logical to suggest that had the U.S. been willing to leave substantial forces in Iraq that Washington might have been able to strengthen the Iraqi military. But so long as then-Prime Minister Maliki was determined to ensure that Shiites ran Iraq and to marginalize the country’s Sunnis, the odds were very grim that the U.S. could have prevented the expansion of ISIS without a major commitment of forces. And without concurrent political reforms to give Sunnis a stake in governing, any military victory would have been fleeting.

It’s fair to argue that President Obama was slow to recognize the rise of ISIS–he famously called the terror organization a “jayvee team.” But stopping the rise of ISIS in Syria would have required a U.S. military, political, and economic commitment on par with nation-building–an approach that even critics of President Obama were not prepared to endorse in the wake of events in Iraq and Afghanistan. Mr. Trump is adamantly opposed to such a policy. But had the U.S. done what Mr. Trump advocated in 2007– declared “victory” and gone home–the door would have been open for jihadists and other extremists of ISIS to become a more powerful force earlier. Mr. Trump’s words make plain that he would have advocated the same policy President Obama pursued in 2011: withdrawal.