Why does Trump want to build a wall? Is it worth?

Recently, President Trump signed a bill averting government shutdown. Moreover, he also declared a national emergency to obtain funds for his long-promised border wall. In opting to declare a national emergency, Trump would seek to access funds for the wall that Congress had not explicitly authorized for the purpose. Previously, Trump demanded 5.7 billion dollars in funding for the border wall. However, in signing the bill, he agreed on 1.375 billion dollars.

But what are the perks in building a wall? According to Trump, by building a wall on the border, it will keep out low-wage workers and, thereby, raise the wages of U.S. workers, and reduce illegal immigration. A wall will probably open the door to reaching a broad agreement on immigration policy. However, the inflow of undocumented Mexican immigrants is slowing and perhaps even reversing. A 2015
Pew study found that the number of undocumented Mexicans in the United States had dropped by 140,000 between 2009 and 2014. Moreover, the southern border isn't the only way people become illegal immigrants. Many arrive illegally and overstay their visas. According to a study in the Journal on Migration and Human Security, these immigrants now outnumber those breaching the southern border. Thus, the question is, is building a wall really worth it? Based on factual evidence, no it's not.