First came the tweet, claiming “Middle Easterners” had infiltrated a group of Central American migrants making their way through Mexico.
Then came the officials and Republican politicians to back Donald Trump’s allegations.
And then - with TV news running his claims about a national immigration emergency - came the backtrack, as Mr Trump admitted he had no proof that people from the Middle East were among the 7,000 or so people in the “caravan” walking towards the US border.
But still he left supporters with a hint of unknown forces at work.
“There’s no proof of anything,” he told reporters in the Oval Office on Tuesday when pushed on the subject. “But there could very well be.”
During the past week Mr Trump has pivoted to the issues that helped him win election in 2016 as Republicans prepare for a midterm vote next month that could see them lose control of Congress.
He has focused attention on the caravan of mostly Honduran migrants that pushed north into Mexico at the start of this week.
Although it is still at least 1,000 miles from the US border, Mr Trump has not held back from raising the alarm.
“Sadly, it looks like Mexico’s Police and military are unable to stop the Caravan heading to the Southern Border of the United States,” he tweeted on Monday. “Criminals and unknown Middle Easterners are mixed in.”
The issue has dominated American media for days. Even news organisations such as the Associated Press have been criticised for using the terms “army” and “crisis” to describe what is a regular - and often little-noticed - event.
White House officials such as Sarah Sanders, the press secretary, backed the president’s claim saying the administration “absolutely” had evidence of Middle Easterners in the caravan.
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So too Mike Pence, the vice-president, who has often avoided being dragged into Mr Trump's rows. "It's inconceivable that there are not people of Middle Eastern descent in a crowd of more than 7,000 people advancing toward our border," he told The Washington Post.
Yet, the president was forced to back away from his incendiary claim on Tuesday evening under questioning.
He said he spoke to Border Patrol officers who told him that they had intercepted many people from the Middle East in the past.
“They've intercepted ISIS. They've intercepted all sorts of people. They've intercepted good ones and bad ones,” he said, before admitting he had no evidence of Middle Eastern participants this time.
The caravan began in San Pedro Sula, a Honduran city with a bloody reputation for gang violence, where about 100 people began congregating on October 11. A political activist sent a flurry of social media messages after hearing from would-be migrants who wanted safety in numbers for their arduous journey.
The result was intense media coverage across Honduras and then Central America, which in turn attracted more travellers.
Such caravans happen frequently but had rarely garnered much attention until this year.
This one reached Mexico at the start of this week. It paused on Tuesday to mourn a traveller who died in a road accident before setting off again at first light on Wednesday morning.
Irineo Mujica, whose Pueblo Sin Fronteras group is helping aid the walkers, said Mr Trump was clearly using the caravan to make border security a major issue in November's midterm elections.
“You could say the one who benefits most is him,” he told the Associated Press. “If the caravan stops, who wins? Him."
Mr Trump has returned to the issue during nightly election rallies. On Monday night, the president described the caravan as an “assault on our country” and claimed (without evidence) that Democrats were behind it.
“We need a wall built fast,” he told his cheering audience in Houston.
As well as closing the border, he is proposing scrapping hundreds of millions of dollars in foreign aid to Honduras, Guatemala, and El Salvador.
Campaigners and analysts said there was no evidence that migrants from the Middle East were in the caravan.
However, Michelle Mittelstadt, of the Migration Policy Institute, said the current procession was different to previous ones and was significantly bigger.
“Second, media attention, particularly by US media, has been intense, and third, you have a White House that has seized upon this issue and is highlighting it relentlessly and raising this to a foreign policy priority with Mexico and the Central American governments,” she said.
