By Mark Austin, chief presenter
Make no mistake, this is a big moment.
Donald Trump has done what he said he wouldn't do 鈥� he's gone to war in the Middle East.
He will be hoping that this will be a short, sharp clinical war for America.
An "in-and-out" war, fought from 35,000 feet with B2 aircraft and their bunker busting bombs that will send a shudder through an Iranian leadership already brought to its knees by Israel.
But when it comes to this type of war, the "in" is much easier than the "out".
The 'what ifs' to come
Of course, Iran may just accept defeat and roll over.
They could decide the game is up and negotiate a way out.
But what if, as they are threatening, they don't?
What if the retaliation is protracted and intense and includes increasing attacks on US interests?
What if US troops are killed and injured at their now, well-fortified bases in the region?
What if Iran closes the Strait of Hormuz, or launches terror attacks against US targets, killing citizens and causing mayhem?
It is entirely possible, then, that Trump gets drawn in further.
What if the Iranians take what remains of their nuclear project yet further underground and go all out for a bomb?
Is this Iraq all over again - only worse?
It does not require a huge leap of imagination to see it could mean the Trump administration feeling compelled to put troops on the ground to finish the job鈥� and possibly the regime itself.
Then it is starting to look like Iraq all over again鈥� only worse.
If regime change becomes the plan, we have been here before.
I saw it firsthand in 2003 in Iraq - and it was not pretty.
In 2002, in the wake of the 9/11 attacks, there were loud voices calling for the toppling of Saddam Hussein and the wiping away of his murderous regime and its supposed weapons of mass destruction.
Neo-conservative figures in the United States saw the opportunity to "revolutionise the power dynamic across the Middle East".
It was widely thought that the people of Syria, and Iran - yes Iran - would simply not tolerate tyranny in their own country once "freedom" had come to Iraq.
In September of 2002, a shaken President Bush said as much himself. "The people of Iraq can shake off their captivity. They can one day join a democratic Afghanistan and a democratic Palestine, inspiring reforms throughout the Muslim world."
How hollow those words look today.
When regimes fall, violent chaos often follows
In March 2003, US and British forces invaded, and I was among many journalists who either went with them or who followed them in.
With my camera team, we crossed the desert border from Kuwait and entered the battlefield of southern Iraq.
Very quickly, it was obvious to me and everyone else that the Iraqi military had neither fought nor surrendered, but rather, they had simply melted away.
They had shed their uniforms but not their weapons. They bided their time, formed their militias, laid mine after mine on ground they knew well, and launched insurgency attacks on the invading armies who were soon wondering what on earth they were doing there.
The regime had collapsed. Saddam Hussein was later found hiding in a spider hole near Tikrit. He was put on trial and executed.
But what replaced him was violent chaos, and Iraq became a deadly hellhole where years of bloody violence claimed the lives of countless troops.
Iran has the potential to be so much worse
Regime change is hard to calibrate. A transition to a stable democracy in Iran would be the outcome most desired by many in the West, but it is not one that can be at all guaranteed.
Where is the political movement waiting to take over?
Where is the leadership in waiting that will bring stability, security and democracy? It is not apparent in Iran.
The worst-case scenario is a chaotic collapse. Rather than a peaceful transition to a new orderly government, more likely is a catastrophic degradation of state institutions and a plunge into wholesale disorder.
In Iraq, it caused years of violent insurgency, posing huge problems for British and US forces.
In Iran, it has the potential to be so much worse. You could well have remnants of the Revolutionary Guards forming militias armed with stashes of weaponry, including missiles and drones.
You could have criminal networks or the much-hated public security police, or both, deciding to make a stand.
Performative presidency just got real
Every war is different, but equally, it is folly to ignore history.
When American bombs are dropped in the Middle East, the consequences are unpredictable and perhaps uncontrollable.
Trump knows that. It is partly why he pledged to keep America out of endless conflicts.
But his determination to put paid to what he believes are Iran's dangerous nuclear ambitions has proved the greater impulse.
He will hope America's involvement ends here. He will be fortunate if it does. But the danger is it won't.
For Trump, this performative presidency just got real.