The need to build a wall along the Mexican border is questioned in a report released Monday showing that, since 2007, there have been more immigrants in the US who came here legally with temporary visas and stayed on after their documents expired than there have been immigrants who crossed the border illegally with no documents.

The Center for Migration Studies (CMS) analyzes in its report the sense of building a 2,000-mile-long wall on the southern US border, one of the chief campaign promises of now-President Donald Trump.

It is also one of the Republican head of state's most criticized decisions for economic, environmental, foreign-relations and human-rights reasons.

Donald Kerwin, author of the study together with Robert Warren, told EFE Monday that the CMS report adds another convincing argument to all those reasons for opposing the wall: official data shows that most new undocumented immigrants no longer arrive secretly over the border but tend to fly into some airport. 

In 2014, says the report entitled "The 2,000 Mile Wall in Search of a Purpose," almost 66 percent of new undocumented immigrants entered with temporary visas and remained in the country after their documents expired or in some other way violated conditions of their entry visas.

That same year, out of a total number of undocumented immigrants in the country, 42 percent entered legally but later stayed in the country after their documents expired.

Kerwin said "it doesn't look like a good idea" to build a wall to stop illegal immigration, if most of the immigrants don't enter the country over the land border with Mexico.

According to CMS, this trend, which began in 2007 and which since then has meant that 600,000 more legal immigrants have crossed the border with US visas than have crossed the border illegally, has paved the way to a very predictable future.

Some 55 percent of illegal immigrants in the US come from Mexico, and Mexicans are "number one" both for crossing the border clandestinely and for overstaying the time limit imposed by their visas.

The decline in the arrival of undocumented Mexican immigrants, which has been observed since 2005, is a key element in the trend to fewer illegal border crossings in general, the Center for Migration Studies said.

Almost all those who have continued crossing the land border clandestinely in recent years have come from six countries: Mexico, El Salvador, Guatemala, Honduras, Nicaragua and the Dominican Republic.

Among those the percentage has increased of immigrants from Central America's Northern Triangle: El Salvador, Honduras and Guatemala.

"Those immigrants are fleeing from persistent violence, persecution and poverty in the area, while a great many of them don't even try to avoid detention but rather hand themselves over voluntarily to border agents and ask for political asylum. Many are genuine refugees," the report says.

California is the state where more people stay on after their visas expire (890,000), followed by New York (520,000), Texas (475,000) and Florida (435,000).