Trump needs to learn another lesson: when a president makes a threat, they have to stand by it.

The White House has announced that Syrian president Bashar al-Assad is possibly preparing to carry out another massive chemical strike.

A press statement says: “The United States has identified potential preparations for another chemical weapons attack by the Assad regime that would likely result in the mass murder of civilians, including innocent children.”

It continues with the threat that if Assad does carry out such a strike, “he and his military will pay a heavy price”.

So far, there’s no knowing on what evidence this statement is based, nor what exact “price” Assad would pay. The White House alleges nothing specific beyond saying Assad is carrying out activities “similar to preparations the regime made before its April 4, 2017 chemical weapons attack” – the sarin attack against the town of Khan Sheikhoun that killed approximately 80 people, and which prompted Donald Trump to order a punitive strike on Shayrat airfield with 59 Tomahawk missiles.

There are some indications that the US is right to be concerned. A security official, described by Reuters as “familiar with the intelligence”, said the US has been monitoring sites in Syria where they believe Assad is hiding chemical weapons. They said there were signs of “abnormal activity” going on at these sites, but that the intelligence is inconclusive.

But other parts of the US security community reacted to the statement with confusion. Five US defence officials openly said they know nothing about the threat or that evidence even exists; one member of US Central Command said he had “no idea” where this threat had come from. Defying routine protocol, the White House apparently issued the statement without first notifying the Pentagon.

Trump doesn’t seem bothered about the threat. Less than an hour after the announcement, Trump launched yet another Twitter broadside about his predecessor, Barack Obama, and not the supposed chemical massacre to come. As for White House press secretary Sean Spicer, he’s hardly a respected chemical weapons expert, still remembered for saying that Hitler didn’t use chemical weapons during World War II.

The apparent dearth of evidence brings back memories of the weapons-that-never-were in Iraq. Trump should learn the lessons of George W. Bush’s administration: military action without concrete grounds runs the risk of disaster and scandal, while responding to unsubstantiated risks leads to unnecessary conflict and undermines the US’s international reputation. This is precisely what Trump has now put on the line.

Put up or shut up

After Obama’s now infamous failure to enforce his own “red line” on the use of chemical weapons, you’d also think that the Trump team would be more cautious about throwing threats around. When Obama failed to take action after Assad did ultimately use chemical arms, the ensuing policy nightmare never left him alone.

Like Obama, Trump hasn’t made a credible or clear threat. And if Assad does use chemical weapons in a mass attack, the president will be forced into action he may not want or isn’t prepared for. Jon Wolfstahl, former senior director at the National Security Council, has criticised the president for putting the US in a difficult position where they have to act – and act big – if another strike occurs.

Trump was relatively quick to order action after the April attack, but that was apparently a one-off mission. It’s also worth remembering that back in 2013, Trump opposed Obama’s threat to intervene in Syria after 1,500 people were killed by a government-ordered sarin strike on Ghouta.

Unpredictable

Trump seems to pride himself on being unpredictable, meaning it’s unclear what he wants (assuming he even knows) and whether he would be willing to live up to the threat he has just made. If he isn’t, this could be disastrous for the US and for Syria.

The threat will also inflame the White House’s already complicated relations with Russia. In true Trump fashion, Nikki Haley, Washington’s ambassador to the UN, lit the fuse with a tweet of her own: “Any further attacks done to the people of Syria will be blamed on Assad, but also on Russia & Iran who support him killing his own people.”

This is seen as the wrong time to upset the Russians, given that the relationship has deteriorated since Trump took power. Daryl Kimball, head of the Arms Control Association, has said that if Trump was going to do something specific about chemical weapons, he should have done it back in April, when things weren’t as tense between the two countries.

Trump needs to learn another lesson: when a president makes a threat, they have to stand by it. At the moment, he seems to be recklessly issuing vague threats via press release without clearly considering the consequences. As we know from both Iraq and Ghouta, this never ends well.