The crowds of 10,000-plus that Elizabeth Warren has attracted lately in places like Seattle, Minneapolis and Manhattan don't happen by accident.
They are the result of the careful collection of information on would-be supporters and a multi-step process to turn that data into rally attendees who often become worth far more to the campaign than simply making for impressive television crowd shots.
There's a science to the art of campaign crowd building. And few places is it on better display than in the well-honed system employed by the Democratic senator from Massachusetts.
Warren's growing rallies have coincided with her rise in Democratic presidential primary polls.
President Donald Trump also attracted huge crowds in 2016. But the ability to stage a massive rally doesn't always translate to Election Day wins.
