John Dickerson is the most aggressive moderator we've seen in the debates so far.

He’s been pressing both Sanders and Clinton hard on foreign policy issues, and hasn’t cut either candidate any slack. It reads as an attempt to really tease out the differences between the candidates: Just how far to the left are each of the candidates, and what do they really believe? It’s the first time this cycle we’ve seen a moderator try to thin the presidential pack. (This, it goes without saying, is a stark contrast to the Republican debates, which look increasingly like a ratings-hungry sideshow in comparison.) It’s worth noting that he’s mostly spared O’Malley from his scrutiny.

Dickerson’s worked in Washington for long enough to know how to play the moderating game—though tonight he’s been pretty obviously aggressive, he’s been known to ask cutting questions in an extremely innocuous way. Perhaps the most egregious example was in 2004, when he caught Bush off-guard during his bid for reelection; it showed up in a Kerry campaign attack ad.

“Mistakes Were Made,” Kerry, 2004

[TEXT: “Mistakes Were Made,” Presidential Press Conference, April 13, 2004]

BUSH: John.

REPORTER: Thank you, Mr. President. What would your biggest mistake be, would you say, and what lessons have you learned from it?

BUSH: Hmm. I wish you would have given me this written question ahead of time, so I could plan for it.