WASHINGTON — The Supreme Court on Monday rejected an appeal brought by Khalid Sheikh Mohammed and two other alleged 9/11 plotters seeking to hold the government to a plea deal it later withdrew.The court action removes one barrier to Mohammed standing trial before a military commission in 2028, where the death penalty is a possible punishment. He has been held at the U.S. base in Guantanamo Bay, Cuba, since 2006.Mohammed is accused of being the ringleader of the plot to crash hijacked planes into the World Trade Center in New York and the Pentagon on Sept. 11, 2001. A fourth plane crashed in a field in Pennsylvania.The other two men who appealed to the Supreme Court were Mustafa Ahmed al-Hawsawi and Walid bin Attash, who are also held at Guantanamo and set to face trial.The three men had agreed to a plea deal with military prosecutors in 2024, signed off on by a military commission judge, that would have given them life sentences.But days later, then-Defense Secretary Lloyd Austin rejected the proposal, saying he had the authority to override the deal.Military courts said he had no such authority but, in an August ruling, the U.S. Court of Appeals for the District of Columbia Circuit ruled in favor of the government, prompting the men to appeal to the Supreme Court.They argued, among other things, that the appeals court had no authority to intervene in the case.The long delay in Mohammed facing trial was caused partly by concerns about evidence obtained via CIA torture.A fourth alleged plotter earmarked for trial, Ali Abdul Aziz Ali, was not involved in the appeal.