Experts say that, under President Trump, airstrikes have surged in Afghanistan, Iraq and Syria, as well as in Somalia. In Yemen, it is unclear to what extent the Americans, as opposed to the Saudi-Emirati coalition, are responsible. In Afghanistan, the number of American strikes that killed or injured civilians more than doubled in the first nine months of 2018 compared with the corresponding period in the previous year and killed more than 150 civilians, according to the United Nations Assistance Mission in Afghanistan.

Mr. Trump has also eroded constraints on civilian casualties.

Since taking office, he has rescinded rules that required the military and the C.I.A. operating outside of hot battlefields like Afghanistan and Iraq to limit their targets to high-level militants rather than foot soldiers. He also, by eliminating an elaborate interagency approval process, gave military commanders more authority to order drone strikes.

Yet, even under the previous rules, no matter how precise the weapons, how careful the planners and how skilled the fighters, mistakes, faulty intelligence, even calculated decisions often led to civilians being killed. The official data ranges from none to maddeningly vague, and the safeguards to mitigate civilian deaths are insufficient.

The military adopted an elaborate system under the Obama administration to minimize civilian casualties, including a requirement that forces have “near certainty” that no civilian will be harmed before launching an attack. But reporting by The Times and others in 2017 showed that the Pentagon had killed far more civilians in Iraq than it acknowledged.

The Obama administration estimated that over its two terms drone strikes had killed between 64 and 116 civilians in 542 airstrikes outside the major war zones. Micah Zenko, co-author of a new book, “Clear and Present Safety,” calculated the real tally at roughly 324.

Drones, for all their faults, are less indiscriminate than B-52s or almost any other weapon. But they are also a seductive tool, potentially tempting presidents and military commanders to inflict grave damage without sufficient forethought.

A lack of transparency and accountability for c ivilian deaths helps enemies spin false narratives, makes it harder for allies to defend American actions and sets a bad example for other countries that are rapidly adding drones to their arsenals. It could also result in war crimes, as some critics have claimed.