Alabama is set to execute death row inmate Kenneth Smith using nitrogen gas, a method that has never been used before in the United States. The US Supreme Court declined to halt the execution, which is scheduled to take place on Thursday. Alabama had previously tried to execute Smith by lethal injection, but the attempt was aborted due to difficulties with inserting an intravenous line. Supporters of the use of nitrogen gas argue that it is a more humane and painless method of execution, while opponents argue that it is experimental and could lead to prolonged suffering. Alabama is the only state that has a protocol in place for using nitrogen gas, though Oklahoma and Mississippi have also approved the method. The legal battles surrounding this case raise important questions about the constitutionality of using new methods of execution and the potential for cruel and unusual punishment.