By law, Ms. Park cannot be compelled to testify. If she declines to appear for a second time, the court can proceed without her. Chief Justice Park Han-chul, who is not related to the president, said that the next hearing would be held on Thursday and that oral arguments would begin regardless of whether Ms. Park attends. Four former or current presidential aides were also asked to testify on Thursday.

“We recognize the weighty significance this case has in our nation’s constitutional order,” Chief Justice Park said. “We will do our best to ensure an utterly fair and appropriate trial.”

Ms. Park has been accused of conspiring with a longtime friend and confidante, Choi Soon-sil, to extort $69 million from South Korean businesses. In its impeachment motion, the National Assembly characterized the money as bribes. The legislature also accused Ms. Park of undermining freedom of the press by cracking down on her critics and of shirking her duty to protect citizens’ lives by neglecting to respond efficiently to a ferry disaster in 2014 that killed more than 300 people.

No South Korean president has been forced out of office through impeachment. The National Assembly voted in 2004 to impeach President Roh Moo-hyun, but the Constitutional Court reinstated him, ruling that his violations of election law were too minor to justify ending his presidency. Mr. Roh did not attend the court’s hearings on his impeachment.

The charges against Ms. Park are much more serious than those Mr. Roh faced, and they have infuriated the public. Large crowds have gathered in central Seoul for the past 10 consecutive Saturdays demanding an end to her presidency. Small groups of protesters gathered Tuesday outside the Constitutional Court, some calling for Ms. Park’s ouster and others supporting her.