South Korea's Constitutional Court began reviewing President Yoon Suk Yeol's impeachment on Saturday, following a National Assembly vote that led to it. Yoon was scheduled for questioning on Sunday as part of a prosecutors' office investigation, but he has not responded. Meanwhile, the leader of his party, who had supported the impeachment, has resigned.

NBC News reports the prosecutors' office asked Yoon to appear for questioning on Sunday as part of an investigation over his failed attempt to declare emergency martial law earlier this month. Prosecutors will issue another summons for the president. 

On Saturday, the National Assembly voted to impeach Yoon, with 204 lawmakers in the 300-member house in favor of the motion and 85 against. Eight votes were declared invalid, while three lawmakers abstained from voting.

The vote comes a little more than a week after Yoon survived an impeachment vote, capping multi-week political turmoil in the country that borders North Korea. This follows Yoon's declaration of the briefest martial law in South Korean history on December 3, lasting only a few hours, after accusing the opposition party of engaging in 'anti-state activities.'

Recall, Yoon said: "I will not give up. I will do my best for our country." And this could be why he failed to appear for questioning on Sunday.

"If Yoon continues to defy requests for questioning in the two inquiries, investigators could ask a court to issue a warrant for his arrest," NBC noted. 

Under South Korea's Constitution, Yoon's impeachment has allowed Prime Minister Han Duck-soo to become interim leader.

Political instability in South Korea led to the resignation of Han Dong Hoon, the leader of Yoon's People Power Party, on Monday morning. 

Han said he does "not regret supporting the impeachment" because the president's use of martial law was wrong. 

"Defending illegal martial law is a betrayal of the country, the people, the conservative spirit, and the achievements of our party that achieved industrialization and democratization," Han emphasized. 

Given that the Constitutional Court will now decide whether to reinstate or remove Yoon, Goldman's Goohoon Kwon and Andrew Tilton provided clients with the possible transition scenarios. That process could take up to six months.

Here's what comes next: 

Newsquawk's latest headlines on the ongoing political turmoil: 

Also, the Goldman analysts warned of another scenario that could unfold: "... muddling through in a political gridlock."