As President Trump considers pulling American forces into a risky and unpredictable new war in the Middle East, it’s time for the legislative branch to step up. U.S. lawmakers should insist the president obtain a new war authorization from Congress before U.S. forces take any military action against Iran.

While Mr. Trump has so far refrained from committing U.S. military support to Israel’s air campaign, he also hasn’t ruled it out. On Tuesday he called for Iran’s “unconditional surrender,” and mentioned the open possibility of killing Iran’s supreme leader, Ayatollah Ali Khamenei, in a statement posted to his social media site.

The Pentagon has already been moving military hardware, including ships and aircraft, toward the Middle East to give Mr. Trump a wider range of options should he decide to join the war. The United States is supporting Israel through other means as well, including defending against Iran’s drone and missile attacks.

But it is Congress’ constitutional right to declare war — not the president’s — despite the wide latitude given to the White House in recent decades to use military force during the war on terror. As Mr. Trump seriously considers joining Israel in this war, it is essential for elected lawmakers to reclaim their responsibility and put their names on record with a vote as to whether they’re willing to send American troops in harm’s way in yet another war in the Middle East.

Since Sept. 11, 2001, presidents have depended on open-ended legal authorizations from Congress to use military force against a wide array of militant groups in at least 22 countries. Days after the attacks on the World Trade Center towers, the Pentagon and elsewhere, Congress passed a law known as an Authorization for Use of Military Force, or A.U.M.F., that President George W. Bush used to invade Afghanistan; a second A.U.M.F. was passed by Congress in 2002 to invade Iraq. President Barack Obama used those authorizations to expand the drone wars to places like Syria, Yemen and Somalia. President Joe Biden later used them to attack Iranian-backed groups in Iraq and Syria nearly a quarter-century later.

In all of those cases, the decisions on when and how to wield U.S. military forces and assets were made unilaterally by the executive branch, sometimes decades after Congress provided its consent, which defies how our constitution was designed. Through the founding document, the president derives the power to direct the military after a formal congressional declaration of war. And yet Congress hasn’t officially declared war since World War II, in 1942.