There’s plenty of reason to believe, in fact, that Bob Mueller and his team of prosecutors in the special counsel’s office are only getting started. Based on news reports, it appears that there are entire avenues of Mueller’s investigation that still haven’t seen the light of day—including a wide-ranging search warrant to Facebook about the influence Russian advertising on the platform during the election, as well active investigations centering around Wikileaks, the Trump campaign’s data company Cambridge Analytica, and campaign advisers like Carter Page, among others.

Plus, both Flynn and foreign policy adviser George Papadopoulos, who also pleaded guilty to a 1001 violation earlier this fall, have evidently provided investigative information significant enough to merit reduced charges—information that has not yet been made public.

Those still-hidden avenues and not-yet-public incriminating information are deeply significant because of one of Mueller’s defining characteristics: He doesn’t do fishing expeditions. Unlike Whitewater prosecutor Ken Starr, whose years-long investigation sprawled far beyond its original mission to look at a failed Arkansas land deal, an examination of Mueller’s career shows that, if anything, he more regularly errs on the side of narrowly interpreting his mission, doggedly and tirelessly pursuing his own assigned task while ignoring ancillary avenues or unrelated troubling behavior.