older voters (repubs) are more likely to answer landline calls and younger dem voters are harder to reach (cell phones, aversion to voice contact instead of text, etc). plus blacks and latinos heavily trend dem and they aint tryna answer no phone calls from a number they dont recognize lol.

a few pollsters i follow on twitter have thrown this theory out there to account for dems consistently overperforming the polling in recent elections.

people talk about the hidden/ashamed trump vote. but they really might be missing the hidden dem/millenial/minority vote.