While the U.S. Supreme Court in July allowed federal authorities to execute three individuals using lethal injection, its rulings did not go as far as greenlighting executions for the nearly 60 prisoners who are currently on death row in federal prisons, several legal experts on capital punishment said.

The Supreme Court did not delve too far into the merits of the underlying legal arguments in its 5-4 per curiam opinion on July 14 that removed a hold on Daniel Lewis Lee's execution and in similar rulings on July 16 concerning Wesley Ira Purkey and Dustin Lee Honken, said John H. Blume, director of the Death Penalty Project at Cornell Law School.

That could provide an opening for attorneys in future cases challenging the federal government's new one-drug protocol, should the lawyers be judicious with their arguments. While Blume believes there is a clear majority of justices who favor preserving the death penalty, he noted that in June, the high court sent back to Texas a capital case involving an individual deemed to have had ineffective counsel.

"It's clear this is a very conservative Supreme Court," Blume said. "At the same time, it's not an unreachable court."

Attention for now has shifted to Keith Dwayne Nelson, the last of four inmates the Trump administration singled out last summer for execution as part of its initial attempt to revive capital punishment on the federal level. Before this month, federal authorities had executed only three inmates since Congress reauthorized the practice in 1988, with the last occurring in 2003.

Nelson is scheduled to be executed on Aug. 28. He was convicted in 2001 of kidnapping, raping and killing a 10-year-old girl. A federal court for the District of Columbia has given Nelson until July 29 to file a motion on how he wishes to proceed with his case, according to court documents.

Kathryn Clune, an attorney with Crowell & Moring LLP who is representing Nelson, could not be reached for comment.

Autopsies of Lee, Purkey and Honken are still pending. Should evidence from the autopsies suggest that they endured flash pulmonary edema, where the prisoner would feel as if they are being asphyxiated before death, legal challenges by Nelson and other death row inmates based on such findings would be all but certain, Blume said.

The federal government had effectively halted executions following a still-pending lawsuit filed in 2005 by several death row inmates that challenged the three-drug cocktail that authorities were using at the time, said Robert Dunham, executive director of the Death Penalty Information Center.

That case, known initially as Roane v. Gonzales, went into hibernation for about a decade, after the federal government had trouble procuring the drugs used in the executions, Dunham said. District of Columbia federal court has blocked the executions of the inmates involved in the case.

Dunham does not believe it is a coincidence that the Trump administration opted to begin its foray into capital punishment by selecting prisoners who were not part of the Roane case. He also finds it curious that all three were white men who were convicted of killing children. Nearly 60% of inmates on federal death row are of color, according to the DPIC.

"This isn't about the orderly administration of the law," Dunham said. "This is about marshaling executions for political benefit in advance of the election."

The U.S. Department of Justice said in June that it planned to move forward with further executions, but has yet to identify specific individuals beyond Nelson, or when the executions would occur. It is also unclear how many additional doses federal authorities may have in hand of pentobarbital, the drug used in the recent executions, Blume said.

While the Supreme Court noted in Lee that pentobarbital has already been used in over 100 executions "without incident," the July executions were the first instances that federal authorities used the drug. The National Institutes of Health describes pentobarbital as a barbiturate more commonly used in low doses as a sedative to treat insomnia, as a pre-anesthetic for surgery, and in animals for euthanasia and anesthesia.

Austin D. Sarat, a jurisprudence and political science professor at Amherst College who has studied the history of lethal injection, says that while the practice is presented as a more humane method of execution compared to the electric chair or the firing squad, it has a history of errors committed by executors, particularly when compared to other methods of execution, such as the gas chamber or even hanging.

Sarat believes there is evidence that while those being injected with pentobarbital may not present outward symptoms of discomfort to observers, the procedure actually causes pain and suffering to a degree that violates the Eighth Amendment's prohibition of cruel and unusual punishment. He notes that the Supreme Court has never struck down a method of execution, having previously upheld electrocution, the firing squad and various methods of lethal injection.

"The fact that the court has found methods of execution to be constitutionally permissible does not end the inquiry," Sarat said. "It doesn't mean that those methods of execution, even if they are constitutionally permissible, are compatible with America's deepest moral and political commitments."

As the Trump administration shifts towards executions, public sentiment suggests the opposite: An annual poll by Gallup on the values and beliefs of Americans found that in May, 54% of U.S. adults believed capital punishment to be "morally acceptable," a decline of 6 percentage points from 2019 and the lowest in the poll's 20-year history. As recently as 2006, 71% of U.S. adults found the practice to be morally acceptable.

In 2019, 60% of Americans preferred a life sentence without possibility for parole for a murder conviction, while 36% preferred the death penalty, according to Gallup. When presented with the same option five years prior, a slight majority of U.S. adults had preferred the death penalty.

Dunham noted that states are also shifting against the death penalty: 34 states either do not have the death penalty or have not had an execution in at least 10 years.

In recent years, Connecticut abolished the death penalty for future crimes in 2012, the Delaware Supreme Court struck down the state's death penalty statute in 2016, the Washington Supreme Court struck down the state's death penalty statute in 2018, and New Hampshire legislators abolished the death penalty for future crimes in 2019, according to the DPIC.

"Both the direction of the administration's policy and the manner in which it has attempted to carry it out have shown that the administration is out of step with the rest of the country and is an outlier in its criminal law practices," Dunham said.

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--Editing by Katherine Rautenberg.