Nearly 16 years after U.S. forces first entered Afghanistan, there they remain. Success, narrowly defined as creating Afghan institutions capable of preventing that nation from once more becoming a haven for terrorists, has proved elusive. Among those noting that absence of success was Trump himself. Prior to becoming president, he denounced the war as a "terrible mistake," a "total disaster," and a "complete waste." In 2013, he tweeted that "We should leave Afghanistan immediately."

Now in the most important foreign policy decision of his presidency so far, he has chosen to perpetuate and to expand the war. Acknowledging that Americans are "weary of war without victory," Trump promised to press on. "In the end," he insisted, "we will win." His commitment to that goal is unambiguous, even if his strategy for achieving it is devoid of specifics. Yet from this point forward, blaming President Obama for whatever happens in Kabul or Kandahar or the Hindu Kush won't work. Afghanistan is Trump's war now.