Does President Trump need Congress to order the bombing of, say, Iran’s Fordow nuclear site? Senator Kaine thinks so and on Monday introduced a resolution that would require the 47th president to secure congressional approval before taking military action against the Islamic Republic. Mr. Kaine’s attempt to curb Mr. Trump comes at what appears to be a crucial moment in the war — one where American support for Israel could prove decisive.

That appears to be Mr. Kaine’s fear. He claims his goal is to avoid embroiling America in “another endless conflict.” His real sentiment seems — at least to us — to be indifference, even hostility, toward an Israeli victory. He demands a “congressional vote” before a strike on Iran. The Constitution grants Congress the power to declare war; yet Mr. Kaine’s resolution concedes that the president has a “constitutional responsibility” to defend America.

Secretary Clinton’s vice presidential pick has long been weak on foreign policy, including on Iran. In 2015, he boycotted Prime Minister Netanyahu’s speech to Congress. In 2017 he opposed Mr. Trump’s withdrawal from President Obama’s nuclear deal with Iran. In 2020 he spearheaded a resolution that purported to direct Mr. Trump to “terminate” the use of our Armed Forces for hostilities against Iran absent congressional vote or war declaration.

For us this issue goes back to Vietnam, into which America plunged on the Tonkin Gulf resolution. That passed the House by 416 to zero and the Senate by 88 to two. The idea was to give President Johnson authority to enter the conflict without a full war declaration. In the event, when the going got difficult, the Democrats turned against the war and eventually forced Congress to halt all support for Free Vietnam, letting the conflict end with a communist conquest.

Congressional dissatisfaction with President Nixon’s handling of the Vietnam conflict led to passage in 1973, over a veto, of the War Powers Resolution. That measure was designed to curb the commander in chief’s power to start, or escalate, a war absent the okay of the solons on the Hill. The law requires the president to notify Congress, within 48 hours, of any military action taken and bars any foreign military deployment for more than 60 days.

America would then go to war in Iraq and Afghanistan without formal declarations but with resolutions that in retrospect were less concerned with achieving victory than with constraining our own forces. That’s the danger in what Mr. Kaine is trying to do. The Constitution, as we read it, doesn’t foreclose authorizations to use military force. The resolutions are, though, much easier than war declarations to betray, as the Democrats showed three times.

The last proper war declarations on which America joined a fight were the ones against Japan and the Axis in World War II. The declaration against Japan bound the president — he was authorized “and directed” — to employ the “entire naval and military forces of the United States” to levy the war. The declaration allowed as how to bring the conflict to a successful termination “all” the resources of the country were “hereby pledged” by the Congress.

The true war declarations were not meant to constrain the president, but rather to liberate him to wage a war to its successful conclusion. So it’s no accident, as we see it, that the modern conflicts America has joined via proper war declarations ended in unambiguous victory, while those we have entered via resolutions fizzled out in either disgrace or surrender. That marks a cautionary point amid today’s debate in Congress over potential action in Iran. 

Which brings us back to Mr. Kaine. “It is not in our national security interest,” he avers, “to get into a war with Iran unless that war is absolutely necessary to defend the United States.” He seems to envision looking, along with his Capitol Hill colleagues, over the president’s shoulder. Yet under the Constitution, who is best positioned to make that determination, especially when military developments are moving rapidly, and often out of public view?