When President George W. Bush began preparing the country for the invasion of Iraq, he traveled the country making the case that Saddam Hussein's government, and its weapons, posed an unacceptable threat to the United States.

Speaking in Cincinnati's Union Terminal one October night in 2002, he warned that Iraq could attack the United States "on any given day" with chemical or biological weapons. He compared the urgency of the moment to the 1962 Cuban Missile Crisis, declaring doing nothing was "the riskiest of all options."

Most of Mr. Bush's arguments turned out to be fanciful, based on selective intelligence and in some cases outright false claims. The war that followed is now considered by many historians as one of the gravest American strategic errors of modern times.

But if Mr. Bush made a false case, President Trump, facing a decision about whether to unleash a second major military assault on Iran in less than a year, has made almost no case at all.

Mr. Trump has never consistently described his goals, and when he talks about them it is usually in a haze of brief, offhand comments. The president has given no speeches preparing the American public for a strike on a country of about 90 million people, and sought no approval from Congress. He has not explained why he has chosen this moment to confront Iran instead of, for example, North Korea, which in the years after Mr. Trump's failed negotiations in the first term has expanded its nuclear arsenal to 60 or more warheads, by U.S. intelligence estimates, and is working to demonstrate they can reach the United States.

Mr. Trump's national security strategy did not mention North Korea once.

And when pressed on Iran, Mr. Trump regularly deflects questions about whether regime change is his true goal, leaving unclear what kind of end-state he seeks -- other than an Iran that can never obtain nuclear weapons.

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Rarely in modern times has the United States prepared to conduct a major act of war with so little explanation and so little public debate. As Mr. Trump gathered the first meeting of the "Board of Peace" at the White House to discuss the rebuilding of Gaza, he veered briefly into the topic of imminent action in Iran, describing only the vaguest of objectives.