Tom Edsall in the NYT:

If you attend an evangelical or a Catholic Church, a women’s rights march or a political rally of any kind, especially in a seriously contested state, the odds are that your cellphone ID number, home address, partisan affiliation and the identifying information of the people around you will be provided by geofencing marketers to campaigns, lobbyists and other interest groups.

With increasing speed, digital technology is transforming politics, constantly providing novel ways to target specific individuals, to get the unregistered registered, to turn out marginal voters, to persuade the undecided and to suppress support for the opposition.

Democrats and Republicans agree that the Trump campaign is far ahead of the Democratic Party in the use of this technology, capitalizing on its substantial investment during the 2016 election and benefiting from an uninterrupted high-tech drive since then.

Republicans “have a big advantage this time,” Ben Nuckels, a Democratic media consultant said in a phone interview. “They not only have all the data from 2016 but they have been building this operation into a nonstop juggernaut.”

The new technology, Nuckels continued, allows campaigns to “deliver a broader narrative over the top” on television and other media, while “underneath in digital you are delivering ads that are tailored to those voters that you need to influence and persuade the most.”