deported to mexico five times. it would have been six, but the san francisco sheriff's department which had been holding him on a drug charge let him go after charges were dropped. why? san francisco is what's called a sanctuary city. it doesn't help federal authorities catch undocumented immigrants. about 300 municipalityies have this designation. san francisco takes it a hardline approach. in the case of sanchez, it released him even though the feds issued a detention request to pick him up. >> a detainer is not a legal instrument. >> reporter: the sheriff defending the policy. >> it makes it safer. we want to build trust with the population. our sangctuary city and other laws have allowed us to do that. >> reporter: tell that to donald trump who seized on the case saying it's "another example of why we must secure our border