The answer is: Casca says that he will also fight Caesar's rise to power.
In Act 1, Scene 3 of Shakespeare's "Julius Caesar," Cassius claims that he could kill himself to free himself from slavery and wishes to abolish Caesar's tyranny. In the same way, Casca agrees by saying that any man can kill himself to accomplish freedom. As a result, Cassius summons him to meet the rest of the men at Pompey's porch in order to carry out Caesar's murder.