When will the U.S supreme court rule the death Penalty unconstitutional?

[True Federalist (진정한 연방 주의자)]

Hopefully not until we have a Constitutional amendment banning the death penalty.  That said, the Court has a sad history of misusing the Eighth Amendment to legislate from the bench. The Eighth Amendment, like the related provisions of the English Bill of Rights, was intended to limit the power of judges, not of legislatures, to decide what penalties to impose for particular offenses.

However, realistically it is useless to hope that the Court will willingly resume giving legislatures due deference instead of choosing to act as unelected legislators. Still, given the current composition of the court, not for at least another two decades, even if the Democrats unpack the Court after the midterms.

After all, the contemporaneous Fifth Amendment lays out requirements for bringing capital cases, so it is ludicrous that the Eighth could be used as a basis for barring capital punishment unless the Court decides to legislate.

[True Federalist (진정한 연방 주의자)]

Not until we have another Warren Court, so not for a long while. Maybe not even in our lifetimes.

But the Warren Court never did strike down the death penalty It was (temporarily) struck down by the Burger Court, in 1972's Furman v. Georgia. The five-man majority in Furman was made up of the Court's three most staunchly liberal Justices -- Douglas, Brennan, and Marshall -- but also two of its relatively moderate Justices -- Stewart and White. So I don't think there has to be at least five staunchly liberal Justices to do what the OP asks.

Except that the death penalty itself wasn't struck down in Furman. It was the manner in which the death penalty was imposed that was struck down. Only Brennan and Marshall went so far as to hold the death penalty was itself unConstitutional. It would require a far more anti-death penalty Court than we have ever had.

(Incidentally, Marshall's concurrence in Furman is one of the most blatant attempts to legislate from the bench, I've ever read.  He outright states "It is immediately obvious, then, that since capital punishment is not a recent phenomenon, if it violates the Constitution, it does so because it is excessive or unnecessary, or because it is abhorrent to currently existing moral values."  He then goes on to usurp the legislative function of determining the popular will by baldly stating without any supporting evidence: "Assuming knowledge of all the facts presently available regarding capital punishment, the average citizen would, in my opinion, find it shocking to his conscience and sense of justice. For this reason alone, capital punishment cannot stand."  It certainly shocked his own conscience and sense of justice, but judges are not average citizens, nor are they supposed to reflect the views of average citizens.  That function in our system lies with the legislative branch, not the judicial branch.

But enough of Marshall and his attempts to legislate from the bench.  For a court to find capital punishment unConstitutional without acting as an unelected legislature, it would have to overturn among other case law In re Kemmler, 136 U.S. 436 (1890): "Punishments are cruel when they involve torture or a lingering death; but the punishment of death is not cruel within the meaning of that word as used in the Constitution. It implies there something inhuman and barbarous -- something more than the mere extinguishment of life." (Bold added by me.) Kemmler was a case concerning whether the then newfangled method of execution by alternating current adopted by the State of New York in place of hanging was Constitutional.  There's also the earlier Wilkerson v. Utah, 99 U.S. 130 (1878) which held using firing squad as a method of executing capital punishment was Constitutional, tho it didn't bother to explicitly hold the death penalty itself as Constitutional the way Kemmler later did.

(The one good thing about Marshall's concurrence in Furman is that it does present a good historical overview of the judicial history of capital punishment in the United States up until that time.)

[True Federalist (진정한 연방 주의자)]

Never. The country is only getting more right-wing.

That's as silly as the 1960s justices who thought history was inexorably heading leftward, so they only needed to give it a push to get there a little sooner. History is not, and never has been, monotonic in any political direction.

[True Federalist (진정한 연방 주의자)]

Hopefully very soon - it's wasteful, inhumane violation of the 8th amendment, and expensive. We need an immediate federal moratorium and eventual abolition.

I've written about this before, but the Supreme Court's misapplication of the Eighth Amendment prohibition on "cruel and unusual punishment" is the clearest example of judicial overreach that is currently going on. (Only the Lochner era treatment of the Fourteenth Amendment is comparably bad.) The prohibition was intended as a limit on the judicial and the executive branches, not the legislative branch. In my opinion, the only valid reason for the court to strike down a punishment under the eighth would be if the prosecution had sought and obtained a punishment that was on the books, but hadn't been used in a long while. That still leaves Fifth and Fourteenth Amendment reasons to strike down particular cases or implementations of capital punishment.

[True Federalist (진정한 연방 주의자)]

Hopefully very soon - it's wasteful, inhumane violation of the 8th amendment, and expensive. We need an immediate federal moratorium and eventual abolition.

I've written about this before, but the Supreme Court's misapplication of the Eighth Amendment prohibition on "cruel and unusual punishment" is the clearest example of judicial overreach that is currently going on. (Only the Lochner era treatment of the Fourteenth Amendment is comparably bad.) The prohibition was intended as a limit on the judicial and the executive branches, not the legislative branch. In my opinion, the only valid reason for the court to strike down a punishment under the eighth would be if the prosecution had sought and obtained a punishment that was on the books, but hadn't been used in a long while. That still leaves Fifth and Fourteenth Amendment reasons to strike down particular cases or implementations of capital punishment.

My take is that the 8th is one instance where the Constitution is a "living document," in that what constitutes cruel and unusual is subject to change as societal morays change. So when most states have banned it, that would constitute a good inditia that it has indeed become cruel and unusual.

That's an extremely subjective opinion, which it should be up to Congress and/or the State legislatures to decide, not the judiciary.  Moreover, your argument presumes that social morays can only change in one way, towards finding certain things cruel that weren't once seen as being cruel.  I completely reject the "evolving standards of decency" thesis, and even if I accepted that, I would still completely reject the idea that it is the judicial branch's role to determine how far standards have evolved. What is cruel is subjective and thus is a legislative matter; whether a particular act meets a particular standard of being cruel is objective and thus a judicial matter.

Trop v. Dulles, 356 U.S. 86 (1958) reached the right result but in the wrong way. Trop's citizenship was defined by the Fourteenth Amendment and could not be abrogated by an Act of Congress. While I would not necessarily go as far as Afroyim v. Rusk, 387 U.S. 253 (1967) in limiting the authority of Congress to revoke naturalized citizenship, since Trop was a natural-born citizen, I don't have to go that far to reach the result of Trop without invoking the Eighth.

[True Federalist (진정한 연방 주의자)]

OK, no problem. We shall just agree to disagree on this one.

Agreed.  I realize that my belief that the judicial branch should be extremely deferential to the other two branches absent a clear Constitutional provision to the contrary is not commonly held. It also means there a quite a few Supreme Court decisions where I agree with the results, but not the means used to achieve them.

[True Federalist (진정한 연방 주의자)]

What do you think about the case People v. Anderson in California?

I think Justice Mosk's concurrence in People v. Frierson (1979) 25 C3d 14, which was heard after Proposition 17 had amended the California Constitution to overturn People v. Anderson is on point, albeit he does make himself abundantly clear that on this issue, his view is: "the people have spoken; damn them!"

The people of California responded quickly and emphatically, both directly and through their elected representatives, to callously declare that whatever the trends elsewhere in the nation and the world, society in our state does not deem the retributive extinction of a human life to be either cruel or unusual.

"Cruelty" is not definable with precision. It is in the eye of the beholder: what may be perceived as cruelty by one person is seen as justice by another. Thus, this court, in ascertaining the permissible limits of punishment, must look in the first instance to those values to which the people of our state subscribe. That as one individual I prefer values more lofty than those implicit in the macabre process of deliberately exterminating a human being does not permit me to interpret in my image the common values of the people of our state.