Arrest leader leaving Congress in rage (7)
I believe the answer is:
engross
'arrest' is the definition.
(thesaurus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for engross that I've seen before include "Occupy attention fully, absorb" , "Absorb, captivate" , "Totally absorb the attention of" , "Rivet" , "Completely absorb" .)