Donald Trump's tweet about Russia and Syria could spark a third World War.
Says who? Well, the US President himself less than two years ago.
In the days before the November 2016 election, the then-presidential candidate said Hillary Clinton's plan for Syria would "lead to World War III", criticising his Democratic rival for being too tough on Russian President Vladimir Putin.
"We're spending $6 trillion dollars on wars in the Middle East, while our own country falls into total disrepair," he said during a speech in Ohio.
"Now Hillary wants to start a shooting war in Syria, conflict with a nuclear power — Russia — which could very well lead to World War III.
"The way she talks about Putin. She's always said she has no idea, but she's always saying — WikiLeaks, it's Russia, and Donald Trump — I have nothing to do with Russia. She said maybe Donald Trump is involved in projects with the Russians. The answer's no."
It's ironic, then, that Trump has just publicly warned Russia to "get ready" for missile strikes in Syria as he slammed Moscow for backing "gas-killing animal" Bashar al-Assad, the country's President.
In an extraordinarily provocative post, the President tweeted that US air strikes would be coming "nice and new and smart" in Syria.
So what's going to happen if the US carries out its threat?
THE DANGERS OF A NEW CONFLICT IN SYRIA
A series of exchanges between Trump and Moscow have raised the stakes for a serious clash between Russia and the United States.
Last night, the President fired off a tweet telling Russia to "Get ready" for missiles fired at Syria, saying they will be "coming, nice and new and 'smart!'"
The tweet, which sent shockwaves around the world, appeared to be a reaction to a quote by a Russian diplomat in Lebanon, who said any US missiles fired at Syria would be shot down and the launch sites targeted.
"If there is a strike by the Americans, then ... the missiles will be downed and even the sources from which the missiles were fired," Russian Ambassador Alexander Zasypkin told Hezbollah's al-Manar TV on Tuesday evening.
It went further than the Russian line put down by Valery Gerasimov, head of Russia's General Staff, who last month said Moscow had information a fake chemical attack was being staged against civilians to justify US intervention.
"In the event of a threat to the lives of our servicemen, Russia's armed forces will take retaliatory measures against the missiles and launchers used," Gerasimov said in a statement on March 13.
After Trump's tweet, the Syrian Observatory for Human Rights — a British-based war monitor with a network of sources on the ground — reported that pro-government forces were emptying main airports and military air bases.
Security experts have warned we can expect the crisis to escalate over coming days.
Dr Malcolm Davis, senior analyst in defence strategy and capability at the Australian Strategic Policy Institute, told news.com.au the tweet had driven the crisis to a new level.
"I think he was clearly sending a message to the Russians, but he has gotten ahead of formal US diplomacy in the process," he said.
"It's certainly driven this crisis to a new level, raising the direct possibility of a US-Russia military clash.
"Trump has in effect challenged the Russians, and the Russians may feel compelled to shoot down incoming cruise missiles launched by the US. So that escalates the conflict."
He likened the escalating conflict to a classic Cold War crisis, with both sides running the risk of escalating the response of the other.
While it's yet to be seen what happens, these back-and-forth responses could take the conflict in a myriad of different directions. "Does the US then seek to neutralise the Russian air defences to allow their missile strikes to get through? Do the Russians follow through with the explicit threat by the Russian ambassador to Lebanon to strike launching platforms, which could include ships at sea? How does the US and its allies respond to that possibility?"
Meanwhile, Turkey's National Defence Minister Nurettin Canikli has warned of an impending war if the US strikes go ahead.
"If an attack occurs against the forces in Syria backed by Russia or there is an attack by the US-supported forces, Russia won't be able to stay away, otherwise it will lose its influence," he said on Ukraine's 24TV.
"So, serious clashes may start. Just one spark may set the entire region on fire and open the door for the conflict."
He called on both the US and Russia to "act with restraint" and on the Assad regimen to "stop supporting terrorist organisations".
Prime Minister Theresa May has bowed to international and domestic pressure and agreed Britain will join France and the United States in a likely military strike on Syria.
She said all indications pointed to Syrian government responsibility for the Douma attack and such "a shocking and barbaric act" could not go unchallenged.
May is ready to give the go-ahead for Britain to take part in military action, and according to the BBC, she will not seek approval from Parliament for it, despite calls from the opposition Labour Party for Parliament to be given a say.
BBC diplomatic correspondent James Landale warned that the bombing could escalate the situation in Syria.
"Slowly but surely, the ground is being prepared for war," he said.