THE HOUSE of Representatives’ adoption of a resolution Thursday barring military action against Iran without congressional authorization is a welcome development, as is the impending Senate debate of a similar measure, spearheaded by Sen. Tim Kaine (D-Va.). We hope this is only the beginning of a wider reassertion of congressional prerogatives relating to the use of U.S. military force abroad.

President Trump’s sudden order to kill Iran’s top general, Qasem Soleimani, brought the United States to the brink of war with Iran on the basis of no consultation with Congress, or even prior notification of Capitol Hill’s top leaders. The administration says no such heads-up was called for, in the face of what it describes as the “imminent threat” Mr. Soleimani posed.

The administration cited a threat of leaks and even now refuses to share much more than sketchy intelligence. Yet there is no indication that Congress has leaked in such situations in the past, or that even a Democratic-controlled House that recently voted to impeach Mr. Trump would try to thwart a good-faith presidential effort to defend U.S. interests or U.S. personnel from an imminent Iranian threat. Indeed, the resolution the House adopted explicitly permits the use of force “to defend against an imminent armed attack.”

In the 21st century, unfortunately, many potential threats will be of the imminent sort; in theory, we are probably seconds away from a Russian cyberattack, and minutes from a nuclear one. This technological and political reality, coupled with the United States’ global role, challenges the pure constitutional ideal, already undermined by the events of centuries, according to which Congress first authorizes war and then the president, as commander in chief, conducts it.

We find this reality especially discomfiting now that the occupant of the White House is an impulsive political neophyte, exuding contempt for legal and political constraints. Yet presidents of both parties, including figures far more thoughtful and qualified than Mr. Trump, have sent the armed forces on consequential operations — President Bill Clinton’s airstrikes against Serbia in 1999; President Barack Obama’s on Libya in 2011 — without clear permission from Congress. Congress has more often than not acquiesced, in part because it would rather not accept the responsibility itself.

In recent years, Congress has passively allowed a variety of new anti-terrorism missions for U.S. troops — in conflicts well-known (the war against the Islamic State in Syria and Iraq) and obscure (a battle against Islamist militants in Niger). The ostensible statutory authority for much of this, the 2001 authorization for the use of force against the authors of the Sept. 11, 2001, terrorist attacks, does not clearly apply to these new situations and is overdue for a legislative update, as Mr. Kaine has maintained for years.

Possibly now he will find more allies in the Senate. More broadly, the task for Congress is to establish clearer limitations on the unilateral presidential use of force except against imminent threats that cannot be dealt with otherwise. Admittedly, defining those limits would oblige lawmakers to enter a politically difficult gray area, one that they have until now found it politically expedient to avoid. The alternative, however, is to abdicate their constitutional role as a check on executive power.

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