Discussion Forum—A Way with Words, a fun radio show and podcast about language

I appreciate some analysis of the syntax of the sentence below (page 145 of Philip Roth's American Pastoral) -- especially, what is the last 'in' doing in there?

Is this masterstroke or blunder or just standard American ?

He did not know what to reach for in his

estimable strongbox of reactions–this boiling up of something so

visceral in with the rhetorical was not the attack he had prepared

himself for.