He said "the immigration crisis in America makes the country poorer and dirtier and more divided.” He didn't say that immigrants make the country poorer and dirtier and more divided.
The immigration crisis in this country is the fact that people are here illegally. They are breaking US laws, crossing the border illegally, and living in this country illegally. The immigration crisis has nothing to do with those who enter this country legally and obtain citizenship in a legal manner.
Therefore yes, the immigration crisis in America is making this country poorer, dirtier, and more divided. And less safe, and more crime, and more drugs, and more gangs, and more sexual assaults and rapes.