But Ms. Park’s lead attorney, Lee Joong-hwan, said there were no legal grounds for impeachment, citing what he called a lack of evidence. He said Ms. Park had made some “trivial” mistakes — like seeking feedback on some of her speeches from Ms. Choi, who held no official post — but that none were serious enough to warrant removal from office.

The most dramatic argument on Ms. Park’s behalf, however, came from Mr. Seo. Besides referring to Christ and Socrates, he argued that the anti-Park rallies had been organized by communists who sympathize with North Korea, a belief held by some of the president’s older, conservative supporters. “Their candlelight protests didn’t reflect the true sentiments of the people,” he said.

Mr. Seo also appealed for “God’s blessings” to protect the court from communist influences. Many of Ms. Park’s remaining supporters are vocal Christians; outside the court on Thursday, a few of them read from Bibles and prayed for the president.

The Constitutional Court had hoped to hear testimony on Thursday from four of Ms. Park’s former and current aides, but only one appeared: Yoon Jeon-chu, the president’s physical trainer and personal secretary. The court cannot compel witnesses to testify, though they can be penalized if they refuse a summons.

Ms. Yoon did not answer many of the prosecutors’ questions, citing poor memory or an obligation not to divulge secrets. But she gave a detailed account of delivering payments for dresses that Ms. Choi had ordered for the president. South Korean news media have alleged that those dresses might have amounted to bribes from Ms. Choi, though the president’s office said Ms. Park had paid for them; Ms. Yoon said she had paid a dress shop for them on Ms. Park’s instructions, though she said she did not get receipts.

If the court removes Ms. Park from office, she would be the first president in South Korea to not finish a full term since the country became a democracy. An election would then be held in 60 days to choose her successor.