When Gen. Michael Flynn marched into the White House Briefing Room to declare that "we are officially putting Iran on notice," he drew a red line for President Trump. In tweeting the threat, Trump agreed.

His credibility is now on the line.

And what triggered this virtual ultimatum?

Iran-backed Houthi rebels, said Flynn, attacked a Saudi warship and Tehran tested a missile, undermining "security, prosperity, and stability throughout the Middle East," placing "American lives at risk."

But how so?

The Saudis have been bombing the Houthi rebels and ravaging their country, Yemen, for two years. Are the Saudis entitled to immunity from retaliation in wars that they start?

Where is the evidence Iran had a role in the Red Sea attack on the Saudi ship? And why would President Trump make this war his war?

As for the Iranian missile test, a 2015 U.N. resolution "called upon" Iran not to test nuclear-capable missiles. It did not forbid Iran from testing conventional missiles, which Tehran insists this was.

Is the United States making new demands on Iran not written into the nuclear treaty or international law—to provoke a confrontation?

Did Flynn coordinate with our allies about this warning of possible military action against Iran? Is NATO obligated to join any action we might take?

Or are we going to carry out any retaliation alone, as our NATO allies observe, while the Israelis, Gulf Arabs, Saudis and the Beltway War Party, which wishes to be rid of Trump, cheer him on?

Bibi Netanyahu hailed Flynn's statement, calling Iran's missile test a flagrant violation of the U.N. resolution and declaring, "Iranian aggression must not go unanswered." By whom, besides us?

The Saudi king spoke with Trump Sunday. Did he persuade the president to get America more engaged against Iran?

Senate Foreign Relations Committee Chairman Bob Corker is among those delighted with the White House warning:

"No longer will Iran be given a pass for its repeated ballistic missile violations, continued support of terrorism, human rights abuses and other hostile activities that threaten international peace and security."

The problem with making a threat public—Iran is "on notice"—is that it makes it almost impossible for Iran, or Trump, to back away.

Tehran seems almost obliged to defy it, especially the demand that it cease testing conventional missiles for its own defense.

This U.S. threat will surely strengthen those Iranians opposed to the nuclear deal and who wish to see its architects, President Hassan Rouhani and Foreign Minister Mohammad Javad Zarif, thrown out in this year's elections.

If Rex Tillerson is not to become a wartime secretary of state like Colin Powell or Dean Rusk, he is going to have to speak to the Iranians, not with defiant declarations, but in a diplomatic dialogue.

Tillerson, of course, is on record as saying the Chinese should be blocked from visiting the half-dozen fortified islets they have built on rocks and reefs in the South China Sea.

A prediction: The Chinese will not be departing from their islands, and the Iranians will defy the U.S. threat against testing their missiles.

Wednesday's White House statement makes a collision with Iran almost unavoidable, and a war with Iran quite possible.

Why did Trump and Flynn feel the need to do this now?

There is an awful lot already on the foreign policy plate of the new president after only two weeks, as pro-Russian rebels in Ukraine are firing artillery again, and North Korea's nuclear missile threat, which, unlike Iran's, is real, has yet to be addressed.

High among the reasons that many supported Trump was his understanding that George W. Bush blundered horribly in launching an unprovoked and unnecessary war on Iraq.

Along with the 15-year war in Afghanistan and our wars in Libya, Syria and Yemen, our 21st-century U.S. Mideast wars have cost us trillions of dollars and thousands of dead. And they have produced a harvest of hatred of America that was exploited by al-Qaida and ISIS to recruit jihadists to murder and massacre Westerners.

Osama's bin Laden's greatest achievement was not to bring down the twin towers and kill 3,000 Americans, but to goad America into plunging headlong into the Middle East, a reckless and ruinous adventure that ended her post-Cold War global primacy.

Unlike the other candidates, Trump seemed to recognize this.

It was thought he would disengage us from these wars, not rattle a saber at an Iran that is three times the size of Iraq and has as its primary weapons supplier and partner Vladimir Putin's Russia.

When Barack Obama drew his red line against Bashar Assad's use of chemical weapons in Syria's civil war, and Assad appeared to cross it, Obama discovered that his countrymen wanted no part of the war that his military action might bring on.

President Obama backed down—in humiliation.

Neither the Ayatollah Khamenei nor Trump appears to be in a mood to back away, especially now that the president has made the threat public.

Patrick J. Buchanan needs no introduction to VDARE.COM readers; his books State of Emergency: The Third World Invasion and Conquest of America, and Suicide of a Superpower: Will America Survive to 2025? are available from Amazon.com. Patrick J. Buchanan is the author of the new book “The Greatest Comeback: How Richard Nixon Rose From Defeat to Create the New Majority.“