WASHINGTON — On the 140th day of the Trump presidency — one for each allotted character on the executive Twitter feed that stayed conspicuously silent all Thursday morning — a very tall man with a very strange place in this very bewildering moment in American history strolled into Hart Senate Office Building 216, shot a quick glance at the masses arrayed behind him and presented a seen-it-all city with something unusual.

In a capital accustomed to overcooked spectacle and insufferable congressional testimony, James B. Comey delivered on the hype.

For about two and a half hours, the room fell into an anxious hush, punctured sporadically by audible emissions of surprise at the remarks of a deposed F.B.I. director with a collection of Trump-branded knives in his reputational torso.

Senators settled into their telegenic gazes, steely but approachable, often whispering to one another as the witness held forth.