Why does Trump want to construct border with Mexico?

 

Trump claims the wall is necessary because mexico is sending illegal immigrants, 'drugs & rapists across the border.
He will build the wall & make mexico pay for it.
In my opinion, it is unlikely but not impossible that he will be able to build the wall as congress is not supporting him for building wall. He needs a lot of money to do that. Furthermore Mexico has refused to pay for the wall and the plan is likely to be blocked by congress in the senate & house of representatives.
Mexican president pena Nieto
Reported that he will not pay for wall, not at all.
In spite of immense amount of money that the wall will cost, its construction could give him serious problems with his Latin American neighbors and the rest of the world.
Addition to it, it is not clear that congress would support this initiative.