It was a deception that would lead to millions of civilian deaths, and the deaths of nearly 60,000 US soldiers. In August 1964 President Lyndon B Johnson solemnly declared that, after two apparent North Vietnamese attacks on US navy destroyers in the Gulf of Tonkin, military action would take place.

Four years later, Senator Albert Gore – father of Bill Clinton’s future vice-president – warned in a closed Foreign Relations Committee session that, “If this country has been misled … the consequences are very great.” His suspicions were correct. The second Gulf of Tonkin attack might never have happened – and perhaps neither did. Communications to make it look like the attack occurred had been falsified. But US policy was already set on a dramatic escalation of the Vietnam war: and here was the perfect pretext.

This week it emerged that the US government is discussing sending up to 120,000 troops to the Middle East for possible military action against Iran. “We’ll see what happens with Iran,” declared President Trump. “If they do anything, it will be a bad mistake.” The principal driving force behind this is Trump’s national security adviser, John Bolton, a man who thinks there is no problem to which the answer isn’t war: in the Bush era, his militarism was too much for the commander-in-chief who laid waste to Iraq. You can see them scrabbling for excuses already: the Trump administration says Iran-backed proxy groups are preparing attacks on US forces in Iraq and Syria, a claim forcefully denied this week by British major-general Christopher Ghika, the deputy commander of counter-terror operations in both countries. The US has blamed Iran, without evidence, for damage to Saudi oil tankers in the Gulf of Oman. Could an Iranian Gulf of Tonkin be looming?

It is easy to dismiss these fears as alarmist. Is Trump not the man who confounded his critics by seeking peace on the Korean peninsula? Trump boasts that he “actually tempers” Bolton; Iran’s supreme leader, Ayatollah Ali Khamenei, states: “There won’t be any war.” As Sanam Vakil, a research fellow at Chatham House, tells me: “Both sides are posturing, sending [threats] back and forth, and I don’t think heading for any direct military interventions.” Bolton, she reassures me, is just one of many voices in the room, and US secretary of state Mike Pompeo himself says that the US is not seeking war.

But, but, but. Trump’s presidential campaign nurtured the myth that he was the “dovish” candidate in contrast to “hawkish” Hillary Clinton (and this is no defence of Clinton, who once crowed that the US could “totally obliterate” Iran). Trump has dramatically increased the use of drone warfare; and he rained down missiles on Syria. He withdrew US support for the successful Iranian nuclear deal in defiance of his then defence secretary and secretary of state, and has sought to throttle Iran with sanctions. US politicians are ramping up the rhetoric: a Republican senator brags that the US could win a war with Iran with “two strikes: the first strike and a last strike”.

A senior Senate aide tells me that the triumph of Bolton’s plans is all too conceivable: Bolton could exploit Trump’s ignorance of policy, an area in which he excels. While any war would not be popular with Trump’s base he could be convinced by Bolton that it is possible to escalate up to a point, then pull back at the brink: but by then it may be impossible to do so. Rightwing thinktanks and broadcasters are already hyping up links between Iran and al-Qaida.

The consequences of an Iranian conflagration should horrify us. Dan Plesch – a specialist at Soas University of London’s Centre for International Studies and Diplomacy – details the US air and naval power potentially ranged against Iran: it’s what one of his colleagues describes as “a tsunami of precision-guided molten metal”. The “lethality of US force”, says Plesch, “to very rapidly destroy military, civil, political and economic infrastructure is hugely underestimated” – and is far greater than in 2003. The US would seek to impose a government-in-exile with no roots in the country; a bloody balkanisation could follow. Iran would mobilise its regional influence – dramatically increased by the Iraq catastrophe – raising the prospect of wider regional conflict.

The risk is already too real for us to wait and see before acting. Pressure must be exerted by the public on US allies to declare their total opposition to any war with Iran, including not permitting their military bases to be used. The mass protests that will greet Trump’s visit in three weeks’ time must include demands that no British support for such a bloody adventure be offered. Feeling blasé about the danger? Well, consider this: all that stands between Bolton’s violent fantasy being executed is Donald Trump himself.

• Owen Jones is a Guardian columnist