I worked for the Obama campaign in NH in 2012. If you lived in Dover/Somersworth/Rollinsford during that period, you probably have me to blame for sending the democratic volunteers who knocked on your door that year.

We knocked on doors early on mainly to collect data. We used fairly sophisticated software that created lists using the responses to in person and over the telephone canvassing questions and combining that with party registration, past voting behavior, and demographic data. The two main lists were possible persuadable voters, and democratic leaning unreliable voters.

Up to about two months before election day, we spent some time on the persuadable voters, going to homes to try to see if we could talk them into voting blue.

After roughly E Day minus 60, all efforts were turned toward people we expected would vote democratic if they voted, but who couldn’t be counted on to always vote. A voter was deemed unreliable if they had failed to vote in a previous election, particularly if it was the last general election, the primary, or the most recent midterm. The goal was to do everything (legally) possible to make sure they planned to actually get the the polls on election day. If they needed a ride, we would get them one. If they needed childcare, we would arrange it. We wanted there to be no chance that they might forget and no excuse for why they could not go.

The tactics were aggressive and annoying to residents, but they delivered undeniable results. No campaign since has really matched the Obama operation’s level of organization and thoroughness.

Even if you don't change people's mind it can provide useful data to the campaigns