The vast majority of illegal aliens enter the US through legal ports of entry. They are brought in by large agricultural businesses using fraudulent papers. These large businesses then donate large amounts to Republican politicians who then make speeches decrying illegal immigration, but do nothing to stop the flood of illegals coming in via legal ports of entry.
If you have any doubts, tell me what the Republican Congress has done to stop illegals entering the country.
This is an issue that you may only know about via propaganda, but I lived on the border for years. I agree that walls in urban areas are useful, but building walls where almost no one crosses is pointless and wasteful.
If you really want to stop illegal immigration, go out to the fields around Bakersfield or Riverside, catch the illegals and put their employers in jail.