South Korea’s Constitutional Court began formal deliberations on Tuesday to decide whether to impeach President Yoon Suk Yeol. The ousted leader has remained aloof, holed up in his fortified presidential compound as he prepares for what aides have called a “siege attack” by up to 1,000 criminal investigators who planned to detain him on sedition charges.

Mr. Yoon has been suspended from office since he was impeached by the National Assembly on December 14 for briefly imposing a state of emergency 11 days earlier. But he refused to back down. Instead, he vowed to “fight to the end” to regain power through a trial at the Constitutional Court and resisted demands to submit to questioning by officials conducting a separate investigation into the sedition charges.

Ongoing efforts to hold Mr. Yoon accountable for declaring martial law and his refusal to cooperate in all investigations so far have left South Korea in political limbo, casting doubt on the resilience of its decades-old democracy.

Constitutional Court has the sole authority to decide whether the parliamentary impeachment was legitimate and whether Mr. Yoon should be formally removed or reinstated. Small but vocal rival groups of citizens engaged in shouting matches on the narrow street outside the court on Tuesday when the first hearing began. The perimeter wall of the yard was lined with flowers sent by supporters of Mr. Yoona.

But Mr. Yoon did not appear: His lawyers said he feared sedition investigators would capture him if he left his presidential compound. The court adjourned after four minutes on Tuesday when it found that Mr. Yoon is not present. It said it would resume its deliberations on Thursday, when it could proceed with or without him.

The court hearing plays second fiddle in the drama surrounding the criminal investigation. When the investigators first visited the residence of Mr. Yoon to serve the arrest warrant, his bodyguards blocked their access with cars, buses and forming human chains. The investigators retreated, promising to return with more officials.

Tensions around the estate – and fears of a possible clash between the president’s bodyguards and police – have deepened in recent weeks. President Mr. Yoon’s security service turned the hilly compound in central Seoul into a fortress, deploying multiple buses and coils of razor wire to block its gates and walls. Riot investigators and police, meanwhile, have worked out a detailed plan to break through the barriers and arrest Mr. Yoon the next time they try to serve a warrant.

On Tuesday, Mr. Yoon’s presidential chief of staff, Chung Jin-suk, compared Mr. Yoon to a leader under siege who “was left isolated in a castle, with no one to help him, while the sun was setting.”

“They have completed their preparations to launch a siege attack,” said Mr. Chung, a former journalist and lawmaker, referring to the police and investigators.

In the first failed attempt to detain Mr. Yoon, about 100 prosecutors, investigators and police officers visited his residence, but were outnumbered two to one by presidential bodyguards and soldiers. For their second attempt, police officials said they were drawing up plans to deploy 1,000 officers, including those who specialize in breaking up drug gangs and other organized crime groups.

Investigators and police met with officials from Mr. Yoon’s presidential security service on Tuesday to discuss how to resolve the standoff. But there was no immediate sign of resolution.

Mr. Yoon’s aides are trying to prevent him from facing the humiliation of becoming the first sitting president to be detained by his own law enforcement agencies, which would take him to his headquarters south of the city.

His lawyers contested the legality of the court order for his detention. Instead, they suggested that investigators question Mr. Yoon at his residence or in a neutral location while he is allowed to stand trial in the Constitutional Court and answer separate sedition charges as a free man.

But most South Koreans want Mr. Yoon arrested and ousted, according to polls.

Mr. Yoon’s last line of defense — the presidential security service — has begun to show cracks: its chief, Park Jong-joon, resigned last week before turning himself in to police for questioning on whether he had committed criminal obstruction of justice when his agency prevented investigators to serve a court order.

The agency said Monday it had suspended one of its senior officials after the official met secretly with police officers. The official is accused of cooperating with police by sharing information about the presidential compound, including its appearance. But the agency said it did not punish anyone for “expressing opinions” during internal meetings, indicating a heated debate among presidential guards over whether it was right to stop fellow government officials from serving the warrant.

The presidential security service is supported by police and military units.

Both the police and the military said they did not want their soldiers and policemen to be drawn into helping to block Mr. Yoon’s detention.

On Monday, Lee Jae-myung, the main opposition leader, called on Deputy Prime Minister Choi Sang-mok, the country’s unelected acting president, to prevent presidential bodyguards from blocking officials from serving the court-ordered order. But Mr. Choi refused to take sides, urging both investigators and the presidential guard to resolve their dispute peacefully rather than by “violent means.”