What metaphor does Henry develop at the end of the first paragraph to describe the inevitable
war ahead? How does he develop it further in
the next paragraph?

The Supreme Court is most likely to be accused of judicial activism in cases involving:  protection of individual rights.

Writing for the conservative group, The Heritage Foundation, Elizabeth Slattery defines judicial activism as "when judges fail to apply the Constitution or laws impartially according to their original public meaning, regardless of the outcome, or do not follow binding precedent of a higher court and instead decide the case based on personal preference."

Cases involving individual rights are likely to elicit charges of judicial activism because the Constitution does not spell out each and every sort of right citizens may have.  New questions come up that were not considered or specified at the time the Constitution was written.  For instance, Roe v. Wade (1973) addressed the question of abortion and an individual's right to privacy.  Obergefell v. Hodges (2015) addressed the legality of same-sex marriage.  Both are cases of individual rights, where the Constitution did not give direct instruction on the issues at stake.  The decisions on those issues, to allow abortion and to allow same-sex marriage, both are criticized by conservatives as instances of judicial activism.