@MentionMachine: Who’s up, who’s down on Twitter?

Reading the Washington Post I was annoyed by a panel at the bottom of my screen with their @MentionMachine tracks the presidential candidates: Who’s up, who’s down on Twitter?. The @MentionMachine tracks Twitter mentions using the Twitter API and also media mentions using Trove. This is real-time social media text analysis. The Washington Post blog page on @MentionMachine argues that “Twitter was the real-time warning system” that could tell us which candidates were trending up or down. I wonder if that is reliably true or only true in selective cases.