He promised to build a more substantial wall on the Mexico -- United States border to keep out illegal immigrants and vowed that Mexico would pay for it .
Trump 's proposed immigration policies were a topic of bitter and contentious debate during the campaign .
Trump promised to build a more substantial wall on the Mexico -- United States border to keep out illegal immigrants and vowed that Mexico would pay for it .
Trump 's proposed immigration policies were a topic of bitter and contentious debate during the campaign .