The United States may be on the cusp of launching military action that would mark the most decisive moment in its near half-century showdown with Iran.

Yet there’s little public debate about what could be a weekslong assault with consequences that are impossible to predict.

There’s no full-court press from top national security officials. President Donald Trump is making hardly any effort to share the rationale for the potential or why military personnel might be asked to risk their lives. And the White House is giving no public sign that it knows what may unfold in Iran if its clerical regime is toppled, an eventuality that could cause enormous reverberations in the Middle East.

The president has made no final decision either way, sources told CNN.

But every day, and following the failure of his tepid diplomacy to make breakthroughs so far, Trump is being dragged inexorably closer to a fateful decision point. The military has told the White House that it could be ready to launch an attack by the weekend, following a buildup of aerial and naval assets, CNN reported. But one source said that the president has privately argued for and against action and has polled advisers and allies on what he should do.

Given the stakes, and the potential risk to American personnel, the lack of a specific public rationale for any war with Iran seems surprising.

This narrative deficit was reflected in the White House briefing Wednesday, ironically on the eve of the first meeting of the president’s Board of Peace. Press secretary Karoline Leavitt was asked the pertinent question of why Trump might need to launch a strike on Iran’s nuclear program, which he has insisted he already totally obliterated in a round-the-world bombing raid last year.

“Well, there’s many reasons and arguments that one could make for a strike against Iran,” Leavitt said, offering no specifics.

Trump’s explanations extend only to repeated warnings that Iran will face the consequences if it doesn’t make a “deal” with the United States. Last week, he said regime change in Tehran might be the “best thing” that could happen.

Ordering the military into battle is the most somber duty of presidents. Their assumption of the highest office comes with an obligation to explain why force might be necessary. And fuzzy thinking could imperil the mission.

Leavitt implied that Americans should just trust the president. “He’s always thinking about what’s in the best interests of the United States of America, of our military, of the American people,” she said.

This would be a thin foundation on which to launch a major war that might end up costing billions of dollars and unknown numbers of American and Iranian lives, and that could trigger huge military and economic repercussions in the Middle East.

It could also worsen Trump’s already stark domestic unpopularity in a midterm election year.

Trump wouldn’t like any comparison with the Iraq war that began in 2003, given its disastrous aftermath. But before that conflict, the Bush administration spent months in a PR offensive designed to convince the country of its later-debunked rationale for the war. It also managed to win congressional authorization for the invasion — at least securing a domestic legal basis for its actions.

If Trump persists in failing to level with citizens and Congress and then takes military action, he will be prolonging a trend of his second term. And he will be leaving himself politically exposed in the event that strikes go wrong.

But it also appears that Trump is emboldened by his successful ouster of Venezuelan dictator Nicolás Maduro in a spectacular operation last month that killed no US troops. His tolerance for risk may also be heightened because the US assassination of Iranian military and intelligence chief Qasem Soleimani in his first term failed to trigger the kind of regional conflagration and Iranian attacks on US allies that some experts predicted.

In recent weeks, Trump’s strategy on Iran has seemed to mirror his playbook in Venezuela, where he amassed a huge naval armada and demanded concessions. This is 21st-century diplomacy backed by aircraft carrier groups and cruise missiles.

But he risks creating a box for himself that it will be difficult to exit with credibility intact if it turns out that his repeated claims that Iran wants a “deal” are wrong.

The kind of deal that Trump can offer Iran may be unacceptable to its clerical regime, whose top priority is perpetuating itself. And a deal Tehran could offer Trump may be one he’d never accept, since it doesn’t want to talk about its ballistic missiles or regional proxy network, which he sees as red lines.

Iranian concessions on a nuclear program that is already severely disrupted in return for sanctions relief would be unacceptable to Trump. He can’t afford politically to emulate the nuclear deal agreed by the Obama administration that he trashed. And lifting sanctions could help the regime survive.

The New York Times quoted Iranian sources as saying that Iran has indicated willingness to suspend enrichment for three to five years in return for sanctions relief. But Dennis Ross, a former US Middle East peace envoy, told CNN’s Wolf Blitzer on Wednesday that this was a symbolic concession. “It’s pretty hard to see them enriching while Trump is still in office. And what they’re seeking is the lifting of economic sanctions, which is a way of … giving them a kind of lease on life.”

The White House may not be telling Americans why it might be time to go to war with Iran. But that doesn’t mean there are not strategic rationales for doing so. In that sense, Leavitt is right.

Trump’s obsession with naming buildings after himself and erecting new ones — such as the planned White House ballroom — suggest he’s increasingly preoccupied with his legacy.

Ending the often-hot cold war with Iran that has bedeviled every American president since Jimmy Carter would secure him a true place in history. And it could put a historic capstone on an estrangement with revolutionary Iran that began with the humiliation of Americans held hostage in 1979-81, which scarred US global confidence and prestige.

Trump might never get a better opening. The regime has arguably never been weaker. Its regional proxies, like Hamas in Gaza and Hezbollah in Lebanon — which were once an insurance policy against an outside attack — have been shredded by Israel.

Iran’s government is facing its worst-ever domestic crisis. It’s clouded by doubt over the revolutionary succession after 86-year-old Supreme Leader Ayatollah Ali Khamenei dies. The economy is wrecked. Desperation recently drove protesters onto the streets amid food and water shortages and grinding economic conditions. The resulting crackdown may have killed thousands. Trump could make good on his pledge to protesters that the US was “locked and loaded” to defend them by toppling the clerical regime.

While Iran may not pose an immediate deadly threat to the US, it has killed scores of Americans in terror attacks and through militias during the Iraq war. Its leaders have long threatened to wipe Israel off the map — a threat that would become even more grave with nuclear weapons. And a stable, democratic and unthreatening Iran would boost the emergence of a new Middle East, powered by the growing global influence of US allies in the Gulf.

Trump would, of course, be a hero of Iranians if he delivered them from repression.

But there are many reasons why he might be smart to blink.

A serious attempt either to decapitate the Iranian regime or to devastate the military capacity of the Islamic Revolutionary Guard Corps and the Basij paramilitary militia would likely require a multi-day air campaign. This could lead to significant civilian casualties. It would raise the possibility of US combat deaths or the capture of US pilots, which could turn into a propaganda disaster.

While some critics have pointed to Trump’s vows to wage no new wars in the Middle East, an Iran conflict would likely not lead to the kind of massive land invasion that turned Iraq into a morass. But as in that war, the best day for the US might be the one when it fires its first shock-and-awe volleys.

It’s also unlikely that any strike against Iran’s clerical leaders would be as clean as the special forces mission that spirited Maduro out of Venezuela.

There is also the problem of what might come next if the revolutionary government were to fall. Failing to anticipate the day after haunted US regime change efforts in Iraq, Afghanistan and Libya this century.

“My question is, after all is said and done, if this lasts for weeks, what happens next?” Colin Clarke, executive director of the Soufan Center told Isa Soares on CNN International. “Then you’re dealing with a power vacuum, then you’re dealing with the potential for insurgency. And, you know there’s a range of states and non-state actors that would look to exploit that.”

Iran, the seat of the ancient Persian civilization, is less plagued by sectarian divides than Iraq, which splintered after the US invasion. But the loss of central authority might be devastating. And the lack of a coherent umbrella leadership for protesters or organized internal opposition raises further questions about a smooth transition. Any US and Israeli joint military action would be certain to include wide-ranging attacks on IRGC facilities and forces. But sources told CNN this week that US intelligence community still believes that the most likely candidate to fill a leadership void would be the hardline guard corps. So ousting theocrats in Tehran might just lead to an equally radical anti-US replacement.

And longer and more complex military action in Iran than in Venezuela with uncertain consequences would increase political pressure on Trump at home amid multiple polls showing majorities of Americans oppose a new Middle East war. It could also test Trump’s bond with the MAGA movement, since he’s spent the last 10 years telling his base there will be no more foreign quagmires.

While officials said that forces would be positioned to strike Iran at the weekend, US action is not guaranteed. The start of the Muslim holy month Ramadan could augur a delay. So could Trump’s annual State of the Union address Tuesday. Trump prizes the unpredictable, so Iran will be on full alert.

But unless Iran capitulates to terms that Trump is still yet to fully explain to the public, more time will not ease the most fateful dilemma yet of his second term.