The world sees US President Donald Trump’s insistence on building a wall on the Mexican border to control illegal immigration to the extent of shutting down the government as irrational, unreasonable and unnecessary. But, the fact is a Mexico-US barrier was approved long ago and a series of vertical barriers along the border aimed at preventing illegal crossings from Mexico were already built. The barrier is not one contiguous structure, but a discontinuous series of physical obstructions variously classified as “fences” or “walls”.

Between the physical barriers, security is provided by a “virtual fence” of sensors, cameras and other surveillance equipment used to dispatch US Border Patrol agents to suspected migrant crossings. As of January 2009, long before Trump came into the picture, the US Customs and Border Protection agency reported that it had more than 930 km of barriers in place. The total length of the continental border is 3,145 km.

Safeguarding the US border, primarily the responsibility of the Department of Homeland Security, has become a contentious issue as many Central American migrants seek asylum in the US. A battle between Trump and Democratic lawmakers over funding for a southern border wall has led to the current crisis. Meanwhile, the deployment of active-duty troops to the southern border reflects a growing militarisation of the area, though their role is constrained by US law.

The National Guard, a reserve military force deployed for a wide range of missions at home and abroad, has been called on by US presidents several times in recent years to assist border agents in tackling illegal immigration and drug trafficking. National Guard soldiers typically operate in their home state and can be called to action by either a state governor or the president.

While the vast majority of apprehended individuals in previous years were Mexican migrants, an increasing number - about one in three - are now asylum seekers from Central America’s Northern Triangle: Honduras, Guatemala and El Salvador. Rather than seeking to evade border patrols, they are turning themselves in, to enter through legal channels. They say they are fleeing gang recruitment, protection rackets, abusive police and inept criminal justice systems, as well as poverty.

Many of these Central Americans have journeyed to the US border in so-called caravans, which offer a degree of protection from predation on the road and frees migrants from contracting with smugglers.

The Trump administration announced in December that migrants waiting for their asylum claims to be reviewed would have to stay in Mexico, with the Mexican government agreeing to offer them visas and work permits. Some have chosen to apply for asylum in Mexico, though they frequently face harm there and the bureaucracy is already stretched beyond its capacity to process claims.

Trump and his administration have warned of Central American gang members and would-be South Asian and West Asian terrorists joining caravans to infiltrate the US.

Trump has argued that a wall along the southern border, along with other security measures, will keep out criminals and halt the flow of illegal drugs. He has called for lawmakers to approve $5 billion to fund the construction of more than 320 km of wall, including new construction and replacements of older barriers, as well as roads and lighting.

As a signatory to the 1967 protocol to the UN refugee convention, the US has committed to providing refuge to people with a “well-founded fear of being persecuted for reasons of race, religion, nationality, membership of a particular social group or political opinion”. Applicants must demonstrate a credible fear that they would be killed or tortured if returned to their home country.

Trump has denigrated the legal right to seek asylum as a “loophole” in immigration policy, subject to fraud and abuse. Border crossers and asylum seekers have been detained under a blanket “zero tolerance” policy that resulted in the government separating children from their parents and keeping the kids in detention. After backtracking from this policy over the summer, the administration is now reportedly considering new measures to deter would-be asylum seekers. One such measure, which would likely face a legal challenge, would present parents with the choice between keeping their children with them in indefinite detention or having them placed in outside custody.

The Build the Wall, Enforce the Law Act of 2018 is a Bill to fund Trump’s wall. Estimated at $23.4 billion, the Bill would amount to the $25 billion projected to complete the larger and fortified wall. The Bill was introduced on October 12 last year by then House majority leader Kevin McCarthy, who stated that in his opinion, “President Trump’s election was a wake-up call to Washington.” He explained that his belief was that “the American people want us to build the wall and enforce the law. Maintaining strong borders is one of the basic responsibilities of any nation. For too long, America has failed in this responsibility”.

The point of walls is to prevent people from crossing into the US undetected. That’s not what most of the families and children who are crossing are doing. They are turning themselves in to the nearest border agent they see on the US side. Not all of them, but a large share, are seeking asylum - seeking to live legally in the US. That’s something they have a legal right to do even if they crossed illegally - and it’s something they could do at a port of entry even if there was a wall across the entire border.

The Trump administration’s specific problem with the influx of asylum seekers isn’t that the agents aren’t catching them - it’s that they can’t quickly deport them and can’t detain them for the entire time until they are deported because of extra legal protections for asylum seekers as well as for children and families.

The administration’s efforts to claim that thousands of terrorists or potential terrorists have tried to cross into the US have been roundly mocked and debunked. TV network NBC found that a total of six known or suspected terrorists were caught trying to come to the US in the first six months of 2018.

The people still coming to the US without papers are, increasingly, what are sometimes referred to as “non-impactables” - people who can’t be affected by the harshness of the typical immigration enforcement regime. Children and families from Central America are coming despite a journey that is often dangerous, and coming despite the possibility that they might not make it. It’s hard to deter people who are already so desperate.

Fear of migrants overwhelming the US, particularly on its border with Mexico, is not special to Trump. For years, the US has been fighting a battle to reduce migrants, asylum seekers and drug traffickers. The Republicans and Democrats have not been much different from each other in resisting migration. The wall may not make much of a difference as old habits are not likely to alter even in adverse circumstances. But the contradiction between what is engraved on the Statue of Liberty and the erection of a wall to prevent desperate people from coming in will not do the US much good. The number of foreigners entering the US may not reduce on account of the wall, but the image of the US as a haven for the needy and the poor will certainly suffer.

It is estimated that nearly 80 per cent of the US population is in favour of the wall proposed by Trump due to the fear of illegal immigrants, asylum seekers and terrorists. More fundamentally, those who have secured citizenship by birth or naturalisation are afraid that uncontrolled immigration will undermine the prosperity and peace of the country. They have the mindset of those who agitate to get into a train, but once they are in the train, like to prevent more from entering. But the truth of the matter is that the US is a migrant country and continued migration is necessary for the country to maintain its development, particularly technology development. For instance, it is estimated that it will take seven to eight years for the US to replace all the techies working there. So, wall or no wall, immigration to the US will continue, but there will be greater selectivity.

The impact of the wall will be that there will be fewer illegal immigrants from South America and the image of the US as welcoming “your tired, your poor, your huddled masses yearning to breathe free” will change.

T.P. Sreenivasan is a former Indian diplomat. The views expressed here are personal.