With this speech, Mr. Trump has taken ownership of the war, which until now he has essentially fobbed off on the Pentagon. Defense Secretary Jim Mattis, told two months ago by Mr. Trump that he could deploy another roughly 4,000 troops to Afghanistan, sensibly declined to do that, at least until the president announced his strategy. Now Mr. Trump has set forth a plan, although it’s hard to dignify as strategy an address in which he said, “We will not talk about numbers of troops or our plans for further military activities.” He seems not to understand that presidents owe it to voters to be transparent.

What we are left with is a set of intentions, which are what? Nothing less than “victory,” he said, because “in the end, we will win.” But what constitutes victory, and will Americans fight on foreign soil until every terrorist is dead? “Attacking our enemies, obliterating ISIS, crushing Al Qaeda, preventing the Taliban from taking over Afghanistan, and stopping mass terror attacks against America before they emerge,” he proclaimed, which seemed a million miles away from his earlier doubts about foreign entanglements. (There was no mention of collateral civilian casualties, which have recently gone up and angered local populations.)

The accounting so far shows that American forces have degraded Al Qaeda. But the Taliban is an indigenous group, and during Barack Obama’s presidency top generals and officials agreed that the Taliban could not be defeated militarily, and must be brought into a political reconciliation process. Mr. Trump gave short shrift to that approach, saying that a successful military effort was a necessary precondition to political reconciliation.