Many of these forces are engaged in counterterrorism operations — against the Taliban in Afghanistan, for instance; against the Islamic State in Iraq and Syria; against an affiliate of Al Qaeda in Yemen. So far, Americans seem to accept that these missions and the deployments they require will continue indefinitely. Still, it’s a very real question whether, in addition to endorsing these commitments, which have cost trillions of dollars and many lives over 16 years, they will embrace new entanglements of the sort President Trump has seemed to portend with his rash threats and questionable decisions on North Korea and Iran.

For that reason alone, it’s time to take stock of how broadly American forces are already committed to far-flung regions and to begin thinking hard about how much of that investment is necessary, how long it should continue and whether there is a strategy beyond just killing terrorists. Which Congress, lamentably, has not done. If the public is quiet, that is partly because so few families bear so much of this military burden, and partly because America is not involved in anything comparable to the Vietnam War, when huge American casualties produced sustained public protest. It is also because Congress has spent little time considering such issues in a comprehensive way or debating why all these deployments are needed.

Congress has repeatedly ducked efforts by Senator Tim Kaine, Democrat of Virginia, and others to put the war against the Islamic State, which has broad popular support but no specific congressional authorization, on a firm legal footing. President Trump, like his predecessor, insists that legislation passed in 2001 to authorize the war against Al Qaeda is sufficient. It isn’t. After the Niger tragedy, the chairman of the Senate Foreign Relations Committee, Bob Corker of Tennessee, has agreed to at least hold a hearing on the authorization issue. It is scheduled for Oct. 30.

Andrew Bacevich, a retired Army colonel who lost a son in Iraq and is a critic of military operations, says that “a collective indifference to war has become an emblem of contemporary America.” The idea that Americans could be inured to war and all its horrors is chilling, and it’s a recipe for dangerous decisions with far-reaching ramifications. There are many factors contributing to this trend:

During earlier wars, including Vietnam, the draft put most families at risk of having a loved one go to war, but now America has all-volunteer armed forces. Less than 1 percent of the population now serves in the military, compared with more than 12 percent in World War II. Most people simply do not have a family member in harm’s way.