Final answer:
The issue standing between Cassius and Brutus is political conflict and mistrust, reflected in their differing motives against Caesar—Cassius's personal grievances and Brutus's principled stance for the Republic.
Step-by-step explanation:
The issue that stands between Cassius and Brutus is a deep-seated political conflict and mistrust. Despite their united front against Julius Caesar, which culminated in the infamous assassination on the Ides of March, the underlying fissures between these two key conspirators manifest in differing motivations and ideals.
Cassius is often seen as manipulative and power-hungry, motivated by envy and personal spite towards Caesar. In contrast, Brutus is portrayed as more honorable and motivated by a sense of public duty—he joins the conspiracy only after becoming convinced that Caesar's death is necessary for the good of the Roman Republic. This dramatic tension is a central element of William Shakespeare's play Julius Caesar, where the personal dynamics between the characters reflect broader themes of freedom and power, honor, and the potential for corruption.