How does the death penalty in America end?

For decades that has been an abstract question. Now there may be an answer in the case of Shonda Walter, a 36-year-old black woman on Pennsylvania’s death row. On Friday, the Supreme Court met to discuss whether to hear a petition from Ms. Walter, who is asking the justices to rule that in all cases, including hers, the death penalty violates the Eighth Amendment’s ban on cruel and unusual punishments.

Ever since 1976, when the court allowed executions to resume after a four-year moratorium, the abolition movement has avoided bringing a broad constitutional challenge against the practice, believing that it would not succeed. In that time, 1,423 people have been put to death.

Yet there is no question that the national trend is moving away from capital punishment. Since the late 1990s, almost every year has seen fewer executions, fewer new death sentences and fewer states involved in the repugnant business of killing their citizens.

In 2015, there were 28 executions and 49 new death sentences, the lowest numbers in decades. Seven states have abandoned the practice entirely since 2004, for a total of 19 that no longer have the death penalty. Many others have not executed anyone for years. And only three states — Texas, Georgia and Missouri — were responsible for almost all of last year’s executions.