The “migrant caravan” passing through Mexico towards the US border is at the centre of a political storm ahead of the impending midterm elections.

Donald Trump has been accused of capitalising on the plight of the convoy of asylum seekers from Central America to stoke anti-immigration fears, with Democrats arguing the president has cynically leapt on the issue as a distraction from the problems of healthcare funding and the future of relations with Saudi Arabia over the killing of journalist Jamal Khashoggi.

The matter has become a defining “wedge issue”, dividing voters as campaigning enters its final days.

The story began when the caravan set off from a bus terminal in the Honduran city of San Pedro Sula in the early hours of 13 October, its participants hoping to find work and a better life in Mexico or the US away from the crime, corruption and poverty of their homeland, notorious for its high murder rate. Much of the killing and corruption is linked to hugely lucrative trade in smuggling cocaine and other drugs into the US.

Crossing first into Guatemala and then Mexico, the group trekked slowly north, attracting more people as it progressed – and, eventually, the attention of the US president.

Mr Trump has repeatedly alleged, without offering any evidence to substantiate the claim, that groups with malign intentions towards the US had infiltrated the procession, which numbered 7,000 participants at its height.

He took to Twitter on Monday to suggest that “Many Gang Members and some very bad people” were present among the migrants and threatened that “our Military is waiting for you!”

Some 5,200 troops have duly been dispatched to the border as a show of force by the president, supporting the 2,100 members of the National Guard brought in in April to protect Texas, New Mexico, Arizona and California after Mr Trump raised concern about an earlier, smaller caravan this spring.

Armed militia groups are also reportedly on the scene, prepared to defend the territory against attack.

These moves follow a tweet on 22 October in which Mr Trump criticised the authorities in Mexico for failing to stop the convoy and again questioned its make-up, saying: “Criminals and unknown Middle Easterners are mixed in.”

Challenged on the legitimacy of this claim by the White House press lobby, Mr Trump was forced to concede: “There’s no proof of anything. There’s no proof of anything. But they could very well be.”

According to Annie Correal, a reporter from The New York Times who met up with the convoy in Huixtla, Mexico, the caravan is actually made up of people of all ages, including the elderly and mothers with infants.

The Independent’s own Andrew Buncombe, reporting from Pijijiapan, Mexico, characterised the group as consisting of “Families pushing toddlers in strollers. A group of skinny young men who say there are no jobs in their country. A young woman from Guatemala being helped by medics by the roadside, her ankle twisted and swollen after six days of walking.”

The caravan’s members are understood to be entirely oblivious to President Trump’s politicising of their ordeal and are simply making the crossing in search of a better future, the undertaking itself a perilous endeavour placing them at the mercy of the drug cartels, human traffickers and corrupt officials en route.

They are travelling en masse because there is safety in numbers and are making no attempt to conceal their presence on the road to the US checkpoint at McAllen, Texas, which would be a logical step for anyone intending to cross illegally.

For his part, the US president has threatened to withdraw aid to Honduras for its failure to prevent the exodus and worked hard to suggest his political opponents are weak on the question of national security compared to his own “zero tolerance” approach to illegal immigration.

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“The Democrats want the caravans, they like the caravans. A lot of people say ‘I wonder who started that caravan?’’’ he told a Make America Great Again rally in Elko, Nevada, on 20 October.

His insistence that Democrats favour “radical socialism and open borders”, which could presumably only lead to lawlessness, has been picked up by Republicans like Ted Cruz in Texas, running for re-election to the Senate, who has attacked challenger Beto O’Rourke along similar lines.

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“The president is desperate to change the subject from healthcare to immigration because he knows that healthcare is the number one issue Americans care about,” Senate minority leader Chuck Schumer and House minority leader Nancy Pelosi responded in a recent joint statement. “Democrats are focused like a laser on healthcare and will not be diverted.”

Seeking to strike a more conciliatory, measured tone in response, Mr Trump has now promised to set up the migrants in “very nice” tent cities when they arrive on US soil.