But while it makes sense to loosen the overly restrictive rules of engagement imposed by the Obama administration, doing so carries risks. A reminder of that came in Syria, where a recent United States airstrike mistakenly killed 18 friendly Syrian fighters. This is not an anomaly; as my Council on Foreign Relations colleague, Micah Zenko, notes, both American airstrikes and civilian casualties have increased since the Trump administration took office.

President Trump, who campaigned on a promise to “bomb the shit” out of the Islamic State militants, will not be concerned about this; indeed, he said that the use of the MOAB was a “very, very successful mission,” and he is probably right, in the narrow tactical sense. But for the bigger strategic picture he would be well-advised to read the 2006 United States Army-Marine Corps Counterinsurgency Field Manual, co-authored by his own secretary of defense, which states: “An operation that kills five insurgents is counterproductive if collateral damage leads to the recruitment of 50 more insurgents.”

Beyond the possibility of collateral damage, there is a larger reason the use of the MOAB in Afghanistan should not be a cause for high-fives and unseemly celebration: It is a sign that the war in Afghanistan is not going well. The kind of war that Vann envisioned — employing small arms — is only possible if the threat is below a certain threshold. When the enemy becomes too powerful, as it did in Vietnam, then it becomes necessary to call in air and artillery strikes. That was not a sign of progress; it was a sign, in fact, that the security situation was spiraling out of control.

The situation in Afghanistan is, needless to say, not nearly as bad as it was in Vietnam during the 1960s. The Taliban are no Vietcong, and they are not supported by regular army units like the People’s Army of Vietnam. But nevertheless the trajectory in Afghanistan has been headed in the wrong direction since President Obama prematurely ended his surge and withdrew most American troops by 2016.